Uamp v0.5.6

It looks like uamp will not have GUI for some time so I decided to merge the current progress to master even though it doesn't have GUI.

Here is list of all the changes since v0.4.0:

v0.5.0

• Option to start playing on start
• Remove gui and related features.
• Add non gui mode for running in background.
• Add options to add newly loaded songs to the current playlist.
• Add option for playlist jump from console.
• Add option to remove songs with non existing paths from library on library
  load, this is enabled by default.

v0.5.1

• Speed up searching for new songs.
• Support multiple arguments at once after instance.
• Add option to start the app in detached mode (run -d).
• Add option to send messages to multiple instances at once.
• Add alternative ways to use actions (-I, -R, ...).
• Add option to print version (--version).
• Handle exit signals.
• Improve info print.

v0.5.2

• Add option to save position within song (save_playback_pos).
• Add secondary playlist.
• Support temorary songs that can exist only in playlist.
• Add option to directly play file.
• Add option to sort the playlist.
• Watch the config file for changes and automatically reload the configuration.

v0.5.3

• Add aliases for control messages.
• Add playlist end actions.

v0.5.4

• Add option to enable/disable color in terminal.
• Add option to set default playlist end action.
• Add option to set add policy as property of playlist.
• Add new add policy: none/- - explicit don't add to playlist.
• Add option to select the sorting complexity from cli.
• Allow unlimited playlist stack.
• Add new filtering options.
• Add new options to edit the current playlist (queue, play-next,
  push-with-cur, flatten)
• Add option to list songs (list)
• Add 1 to playlist position when displaying with -Info (so it starts from 1
  instead of 0)
• Log playback errors.
• Fix overflow in -Info
• Fix bug where some audio files wouldn't play.

v0.5.5

• Add new functionality to filters (and, or, brackets).
• Add shorter aliases for sorting and filtering.
• Add option to sort songs as part of query
• Add terminal friendly alternatives for descending order.
• Aliases can have arguments.
• Print portion of playlist with i nfo
• Print more information about playlist with i nfo
• Fix bug where playlist would panic when removing deleted songs.

v0.5.6

• Add ordering same for no ordering.
• Add port aliases default, debug and release.
• Add new action config to show and edit configuration.
• Add new actions for shell features.
• Add tab completion. Can be enabled with `uamp sh tab`.

• Show volume in i nfo.
• Better errors.
• Propagate errors much further.
• Allow to reverse reverse ordering.
• Allow empty ordering in query.
• Split help to more categories. Don't automatically show help for related
  categories.
• uamp --version now prints only the app id and version.
• Help now prints the app id instead of just uamp in the welcome.
• Allow to specify length of playlist to show for i nfo.

• Fix displaying of playlist position (should start from 1, not 0).
• Fix occasional panic when mixing new songs to playlist.
• Fix issue when uamp wouldn't exit when save is due.
• Fix issue when some temporary songs might not play.