Improved Vim setup

 - Add powerline fonts
 - New plugin : vim-airline
 - New plugin : vim-fugitive
 - New plugin : vim-gitgutter
 - New plugin : syntastic
 - New plugin : emmet-vim
 - New syntax : vim-javascript-syntax
 - New syntax : vim-json
 - New syntax : vim-coffee-script
 - New syntax : vim-for-php5
 - New syntax : Sass
 - New syntax : vim-markdown
 - New colorscheme : github-theme