Add vim-signify; remove vim-gitgutter

References #488.
add fullscreen mode for GVIM and Terminal
add bufferline, work well with airline
change airline theme, match with solarized theme
Merge pull request #498 from JoveYu/3.0

some useful configuration
Merge pull request #489 from mhinz/add-signify

Add vim-signify; remove vim-gitgutter
Merge remote-tracking branch 'spf13/3.0'
unmap F11, and set airline theme