Add support for user configuration

[moverest]

The aim of this MR is for the user to be able to set their configuration through the a configuration file and CLI parameters.

For example, the file would look like this:

[mode_tile]
label_color=#fffd
label_select_color=#fd0d
selectable_bg_color=#0304
selectable_border_color=#040c

The program would look for the configuration file in these places:

• $XDG_CONFIG_HOME/wl-kbptr/config
• ~/.config/wl-kbptr/config
• /etc/wl-kbptr

The same configuration could be passed (or overridden) by passing options to the CLI like so:

wl-kbptr \
  -o mode_tile.label_color=fffd \
  -o mode_tile.label_select_color=fd0d \
  -o mode_tile.selectable_bg_color=0304 \
  -o mode_tile.selectable_border_color=040c

TODO

This MR

• [x] Define configurable parameters
• [x] Define defaults
• [x] Make use of configuration:
  • [x] Tile mode colors
  • [x] Bisect mode colors
  • [x] Keybindings
• [x] Parse configuration values
• [x] Parse CLI arguments

Subsequent MRs

• Parse configuration file
• Documentation and discoverability
• Tests
• Improved error handling