Switched from vim-powerline to vim-airline. Updated all submodules.

	modified:   .gitmodules
	modified:   bundle/clang_complete
	modified:   bundle/ctrlp.vim
	modified:   bundle/gist-vim
	modified:   bundle/nerdtree
	modified:   bundle/syntastic
	new file:   bundle/vim-airline
	modified:   bundle/vim-fugitive
	modified:   bundle/vim-indent-guides
	modified:   bundle/vim-markdown
	deleted:    bundle/vim-powerline
	new file:   vim-airline
	modified:   vimrc
	modified:   zshrc