update doc.
upgrade all funcrefs to support varargs.
improve vim-signify integration (#169).
autoload external extensions (#170).
Fixes bundle paths. For example ftbundle add 'vim-airline/./autoload' into RTP.
Merge pull request #171 from mattn/fix_bundle_paths

Fixes bundle paths. For example ftbundle add 'vim-airline/./autoload' in...
Don't use name 'vim-airline' to check loadable extensions. Someone may git clone as another directory.
Merge pull request #172 from mattn/check_loadable

Don't use name 'vim-airline' to check loadable extensions.
fix regression; account for symlinks.
Better toggling of powerline fonts

+ Check the value of airline_powerline_fonts not just existence
Merge pull request #174 from jacobwalker0814/powerline_fonts

Better toggling of powerline fonts
add screenshot for customization.
break early implicit if return code is not 0.
fold exclude funcrefs into the default one.
pass builder into statusline funcrefs.
pass arguments into funcrefs properly.
remove function call, no longer needed.
document the pipeline.
add screenshot about pipeline.
introduce g:airline_theme_patch_func (#173).