Fix #417
Use eval in tmux/powerline.conf

fish does not support variables used as commands
Add note about POWERLINE_COMMAND to documentation
Merge remote-tracking branch 'zyx-i/auto-use-powerline-client' into develop
Merge remote-tracking branch 'kovidgoyal/fix-417' into develop
Fix committing with fugitive => stuck file status

Fixes #482 (I hope)
Merge remote-tracking branch 'kovidgoyal/fix-482' into develop
Revert "Fix committing with fugitive => stuck file status"

This reverts commit 0435d44984d06f4fada20e3d6df9b5bd2f601f16.

The commit introduces a huge performance penalty and is removed for now.
Add powerline/bindings/fish/powerline.fish