Replace a few instances of "mermen" with "merfolk" in core descriptions

These are only the ones were it's sufficiently unambiguous that the
description is referring to the merfolk race at whole. There are a few
instances I didn't touch were it's possible that the text refers
exclusively to mermen fighters (e.g. "the mermen armies").

See issue #2940.

[ci skip]

(cherry-picked from commit 14ec995)

changelog.md

@@ -47,7 +47,8 @@
  ### Packaging
    * OpenMP support has been removed. It is no longer an optional build-time dependency.
  ### Units
-   * Changed the plural name for the merfolk race from Mermen to Merfolk (issue #2940).
+   * Changed the plural name for the merfolk race from Mermen to Merfolk (issue #2940)
+     and replaced a few instances in core unit or terrain descriptions accordingly.
  ### User Interface
    * Swapped the position and formatting of game names and titles in the MP lobby.
    * Made Faction Select button's purpose more clear in MP Staging.

data/core/terrain.cfg

@@ -2824,7 +2824,7 @@ Most units receive 20 to 40% defense in sand."
     help_topic_text= _ "<italic>text='Coastal reefs'</italic> are shallows formed by stone, coral and sand.
 This provides most land units with a more steady footing and defensive positions than wading in shallow water normally would and also grants most water-dwelling races an exceptionally high defense.
 
-Mermen and Naga both receive 70% defense on coastal reefs."
+Merfolk and Naga both receive 70% defense on coastal reefs."
     hidden=yes
 [/terrain_type]
 
@@ -2853,7 +2853,7 @@ Most units have about 50% defense in hills, whereas cavalry are limited to 40%.
     help_topic_text= _ "<italic>text='Swamps'</italic> represent any sort of wetlands.
 Swamps slow down nearly everyone, and inhibit their ability to defend themselves. An exception to this is any race bodily skilled in navigating water; these receive both full movement and a defensive bonus. Those that make their living in the wetlands are also adept at using this terrain for cover.
 
-Most units make do with 30% defense in swamps. Mermen, naga, and saurians all generally enjoy 60%."
+Most units make do with 30% defense in swamps. Merfolk, naga, and saurians all generally enjoy 60%."
     hidden=yes
 [/terrain_type]
 
@@ -2865,7 +2865,7 @@ Most units make do with 30% defense in swamps. Mermen, naga, and saurians all ge
     editor_name= _ "Shallow Water"
     help_topic_text= _ "<italic>text='Shallow water'</italic> represents any body of water deep enough to come up to roughly a man’s waist. This is enough to slow down nearly anyone and leave them wide open to attack. Dwarves, given that the water reaches up almost to their heads, have an extremely hard time of this. The exception is any race whose bodies naturally lend themselves to swimming, for which they receive a considerable defensive bonus and full movement.
 
-Most units make do with 20 to 30% defense in shallow water, whereas both naga and mermen enjoy 60%."
+Most units make do with 20 to 30% defense in shallow water, whereas both naga and merfolk enjoy 60%."
     hidden=yes
 [/terrain_type]
 
@@ -2907,7 +2907,7 @@ Most units receive about 60% defense in mountains, whereas Dwarves enjoy 70%."
     help_topic_text= _ "<italic>text='Deep water'</italic> represents any body of water deep enough to cover a man’s head.
 Most units cannot enter deep water: it is the domain of units which can either fly, or are exceptionally strong swimmers.
 
-Mermen and naga both receive 50% defense in deep water, with full movement."
+Merfolk and naga both receive 50% defense in deep water, with full movement."
     string=Wdt
     hidden=yes
 [/terrain_type]

data/core/units.cfg

@@ -346,7 +346,7 @@ Trolls have inhabited the mountains of the Great Continent longer than the dwarv
         plural_name= _ "race+plural^Undead"
         description= _"Undead are not really a single race of creatures, although often treated as such. Almost any dead creature can, by a sufficiently skilled necromancer, be reanimated and rise again in undeath. Undead are for the most part unnatural but mindless constructs, obeying whoever created them without question nor thought. A greater mystery of necromancy is in how constructs are sustained without continuous effort from the necromancer. An undead creature does not require the constant attention of the necromancer to command and sustain, but can work autonomously according to the commands of its master. Only rarely, perhaps once every few months, does the necromancer need to maintain his creation.
 
-Necromancy is almost solely limited to humans. Even the legends of magically apt races like elves and mermen tell of very few of their kind who have ever delved in the dark arts. It is surmised that necromantic magic requires great adaptability and a flexible mind, extremes of which are most commonly found in humans. The ultimate goal of most necromancers is to turn the same art of preserving and imbuing life upon themselves, to alter themselves at whatever cost, to ultimately escape death by preserving their own mind and spirit.
+Necromancy is almost solely limited to humans. Even the legends of magically apt races like elves and merfolk tell of very few of their kind who have ever delved in the dark arts. It is surmised that necromantic magic requires great adaptability and a flexible mind, extremes of which are most commonly found in humans. The ultimate goal of most necromancers is to turn the same art of preserving and imbuing life upon themselves, to alter themselves at whatever cost, to ultimately escape death by preserving their own mind and spirit.
 
 <header>text='Geography'</header>
 While undead lords arrived on the Great Continent in considerable numbers only in the wake of Haldric I, they were not completely unheard of by elves and dwarves before that."

data/core/units/merfolk/Priestess.cfg

@@ -18,7 +18,7 @@
     advances_to=Mermaid Diviner
     cost=38
     usage=healer
-    description= _ "Among mermen, mysticism is generally left to the mermaids, who are more inclined to it. It is they who dedicate themselves to the ideal of bringing peace and life to the world, and to the arts which make that possible. Their piety also grants them certain powers, allowing them to guard their people against magical or unnatural things."+{SPECIAL_NOTES}+{SPECIAL_NOTES_MAGICAL}+{SPECIAL_NOTES_ARCANE}+{SPECIAL_NOTES_CURES}
+    description= _ "Among merfolk, mysticism is generally left to the mermaids, who are more inclined to it. It is they who dedicate themselves to the ideal of bringing peace and life to the world, and to the arts which make that possible. Their piety also grants them certain powers, allowing them to guard their people against magical or unnatural things."+{SPECIAL_NOTES}+{SPECIAL_NOTES_MAGICAL}+{SPECIAL_NOTES_ARCANE}+{SPECIAL_NOTES_CURES}
     die_sound=mermaid-die.ogg
     {DEFENSE_ANIM "units/merfolk/priestess.png" "units/merfolk/priestess.png" mermaid-hit.ogg }
     [abilities]