v0.15.0

added and improved help
remapped a few keys and renamed a few settings in the process, see Changes

New features:
- help (F1)
  commit 10ce969dbeb83c64bf24fa77d0f5b4cce2be3f58
- --version shows the version of gitu itself, too
  commit d6f485127203f8d84e74bc1df6b78d1f7cfb6c8a
- add-editor
  commit b0225eb80155263ef14c8f9366c52bfefc645e02
- highlight commands and keys in help
  commit 6c733574b99a520082b2c064abfc85a21e6af6f5
- link commands to their help [WIP]
  commit e0135ad4925e2bb8fd66e10994ad59b2e46e80f5
- help --settings
  commit e9950d8d07df0a13873fbf7f8411383b8456dbd4
- show colors in related settings of link
  commit bea02fdcf9e3302b07d53e78ec38705052f97cf9
- new shortcut C: show more context lines
  commit 1940a24b2c9012da8fd84c326d100f8ee77327c9
- help --cmd
  commit bdc08968838150e19b203c8f7b12c24d63cc5036
- improved help of some commands, e.g. go
  commit eabb6e2a62a7471399680836f9ba8354735c60d5

New settings:
- color.help.key
- color.help.cmd
- color.link.cmd
- link.hint-alphabet
- link.hint-pattern
- help.key-sep
- help.pattern.cmd-with-key
- help.pattern.cmd-without-key
- help.show-all-shortcuts

Bugfixes:
- help for link command
  commit fec248cacb7f35cbdc247dc89597f98d160f3e21
- possible usages in help of primitive commands are not empty when opened from list of keyboard shortcuts
  commit e5fb6c02466fbf906b978dcc56162ac276882f6e

Changes:
- remapped keys for list of keyboard shortcuts and list of commands
  commit 10ce969dbeb83c64bf24fa77d0f5b4cce2be3f58
- remapped key for `linenumber --toggle` to X
  commit 49c60ffabc976292a2002e8ebe5d74aa0a8ab7fe
- renamed setting: color.link -> color.link.hash
  commit b972de614fa6490ebc88208a0d4c12c37e89c764
- renamed setting: color.link-hint -> color.link.hint
  commit bea02fdcf9e3302b07d53e78ec38705052f97cf9
- renamed setting: color.line-numbers -> color.linenumber
  commit 6ee96d554593d735553a89a85241c26cf4eb1a8b

- show shortcuts for fallback commands, too
  commit 0ba9859fa9b0a65bfd8a941413438b142efdb4a3
- show keys first
  commit 8c0ed8b50dfe33346e404806049c84dc59deb860
- show all shortcuts in help
  commit a846c081e44f30ed6e481aeba8d420e39fa23df3