feat: welcome message and string functions edits

[EttyKitty]

Done:

The welcome message:

• Fixed wrong names due to wrong array indices.
• Added units that were missed from the listing: Champions, Librarians, Sergeants, Veteran Sergeants.
• Edited bits of text a little and changed some formatting, so it's more nice and readable (I hope).
• Increased the amount of info on each page after the first, removing the need for the 4th page.
• Fixed equipment list starting at index 1, causing it to skip items at 0 index (bolt pistols, most of the time).
• Various fixes to words using/not using plural forms when required.

Code:

• Various minor refactors, style edits, etc.
• Replaced a lot of string concentration with interpolation.
• Extremely prevalent use of string_plural.

Functions:

• Moved all string functions into one file, "scr_string_functions", just like "scr_array_functions".
• Placed handle_exception into all (most?) catch. Should work like a light version of try_and_report.
• string_plural now supports a second argument - variable to check to decide whenever to convert a string to plural form or not.
• New function integer_to_letters - converts an integer to a string word. Supports 2 additional arguments - capitalize the first letter of the resulting word; output an ordinal form of the word.

Notes:

• Originally tried using int to word function, but decided that while more immersive, it's a bit less readable. Still not sure about it.

TODO:

• Fill documentation on all string functions.
• Rename integer_to_letters into integer_to_word.
• Fix total page count showing 4 pages, even though there are 3.

[OH296]

made one point but probably outside of scope for pr

[OH296]

in general while messing around would be best to sling these in try_and_report_loop maybe?

[EttyKitty]

in general while messing around would be best to sling these in try_and_report_loop maybe?

I think try/catch and handle_exception combo should do the same thing.
I've created handle_exception as a light version of try_and_report_loop, for cases where you don't need custom functions to run on catch. It's just more compact, but works mostly the same way, I think?

[OH296]

i guess that's true, i suppose i was mostly just thinking that try_and_report_loop("ui Manage"), scr_ui_manage) is just less lines and coudl have as you say a custom catch function, but it's probably outside of scope for this pr