Add incremental search in commands history

[flashcode]

Feature description

Add a way to perform an incremental search in commands history, like Ctrl+R in Bash.
This is similar to the script https://github.com/weechat/scripts/blob/master/python/histsearch.py.

Proposed changes (comments are welcome if you have other ideas):

• Move current key Ctrl+R (search in buffer lines) to Ctrl+S
• Add option search_history in command /input, bind default key Ctrl+R on this command
• Add key context "histsearch" (search in commands history)
• Default keys in context "search":
  • return: stop search here (unchanged)
  • ctrl-q: stop search and reset scroll to its initial value (unchanged)
  • meta-c: switch case sensitive/insensitive (unchanged)
  • ctrl-x (instead of ctrl-r): toggle between string and regex search
  • ctrl-r or up: search in previous (older) buffer lines
  • ctrl-s or down: search in next (newer) buffer lines
• Default keys in new context "histsearch": almost the same as context "search":
  • return: stop search and use matching input
  • ctrl-q: stop search and restore input to its initial value
  • meta-c: switch case sensitive/insensitive
  • ctrl-x: toggle between string and regex search
  • ctrl-r or up: search in previous (older) history entries
  • ctrl-s or down: search in next (newer) history entries
  • ctrl-o: execute the command found and put the next one (newer) in input without executing it
• New key in "default" context:
  • ctrl-o: execute the selected command in history (by using keys up/down or ctrl-up/ctrl-down and put the next one (newer) in input without executing it
• New option weechat.look.buffer_search_history: enum with values local (default) or global: default search in history: in buffer local history or global history
• Buffer variable text_search, new possible values are:
  • 0: search disabled
  • 1: search in buffer lines (Ctrl+S)
  • 2: search in commands history (Ctrl+R)
• New buffer variable text_search_direction: enum, possible values are:
  • 0: search backward
  • 1: search forward
• New buffer variable text_search_history: enum, possible valued are:
  • 0: none (search not enabled)
  • 1: search in local history
  • 2: search in global history
• New buffer variable text_search_ptr_history: pointer to history found
• Display in input: prompt + input + matching history entry, for example:

[Search command (~ str,local)] wee█ => /join #weechat