Add `leader version` and fix various bugs

Added

• Added leader version command to output the current version of leader. This is necessary to help
  people who report issues on Github.

Fixed

• Fixed crash when pressing \ in bash anywhere but on an empty command line
• Fixed looping keys nested under the same key going to the parent menu: e.g. j j where the second
  j is listed under loopingKeys actually listed the menu of the first j.
• Fixed configuration file load order: less specific configuration files were loaded after more
  specific configuration files (except for $HOME/.leaderrc), which broke expected configuration behavior
• Fixed @KEYS to execute a command if any of the characters in KEYS point to a key that is bound to
  a command instead of a key map.