update gitgutter plugin
update the "Tag List" plugin to version 4.6
add vim-gitgutter doc
add vim-airline plugin

https://github.com/bling/vim-airline

a#	new file:   .vim/autoload/airline/util.vim
add Powerline fonts

https://github.com/Lokaltog/powerline-fonts
add the command line to install Powerline fonts
add gnome-terminal config
enable airline_theme with nice fonts
remove .netrwhist