Improved documentation on formatters
Improved documentation on formatters

Explains how unique_tail and unique_tail_improved delegate formatting of already-unique filenames to default.
vim-IDE/vim-airline,rchicoli/vim-airline,wilywampa/vim-airline,dalguji/vim-airline,blueyed/vim-airline,tafryn/vim-airline,zekzekus/vim-airline,kazuoteramoto/vim-airline,chrisbra/vim-airline,dlanileonardo/vim-airline,mildred/vim-airline,sappo/vim-airline,yzhou61/vim-airline,HarmtH/vim-airline,bling/vim-airline,unphased/vim-airline,tschundler/dotfiles,tschundler/dotfiles,tschundler/dotfiles