Implement input (command) history with categories

[chros73]

Implement input (command) history for input prompts (e.g. with ^X), as in bash (without searching capability) with categories (mainly because of the upcoming temp-filter feature rakshasa#519):

• all the different input types have their own history:
  • load_default, load_modified, change_directory, command, filter

Functionality:

• entry won't be added to a category history if it's:
  • empty
  • the same as the previous entry
• earlier entry will be updated if it's changed while moving "away" from it and not "applying" it
• last (temp) entry is remembered (until the next prompt)
• history is saved during session.save into session directory (if it exists) as rtorrent.input_history
• history is loaded at startup (if it's available)
• latest entries are kept during resizing history categories if it's smaller than original

Added keyboard shortcuts at input prompt:

• up arrow, ^p : prev in history category
• down arrow, ^n : next in history category
• ESC, ^[, ^g (latter was already defined): exit from input prompt
  • ESC was "used" to mimic ALT at input prompt back in the days but it isn't used there anymore, hence the removal of the code from TextInput.

Added commands:

• ui.input.history.size.set : set size of every history category to this value
  • default is: 30
• ui.input.history.clear : clear all the history categories

Sample rtorrent.input_history file:

1|301
1|302
1|303
3|/mnt/rtorrent/various/
3|/mnt/rtorrent/unsafe/
4|session.save=
4|uptime=
4|print=ok
4|method.insert = try_to_print, simple|const, "print=9"
5|book.*pdf

Existing keyboard shortcuts at input prompt (for reference):

• ^L : force redraw display
• ^Q : normal shutdown
• TAB : path completion at change_directory prompt
• BACKSPACE, ^H
• DEL
• left arrow, ^B : move 1 char to left
• right arrow, ^F : move 1 char to right
• HOME, END
• ^U : erase from cursor to beginning
• ^K : erase from cursor to end

Implementation notes:

• use prefilled ring buffers for each category in history
• keep track of insert pointers for each category in history
• it's enough to store one last (temp) entry and get pointer for all the categories in history

[chros73]

• change default ui.input.history.size.set to 99 (30 was small in practice)
• add ui.input.history.size as a getter command for the sake of completeness

Note: original post is also changed.