Add .ctags file

This file is used by exuberant ctags whenever building tags for code. I
included support for CSS and SCSS[1], since ctags does not support this
out of the box.

[1]: http://stackoverflow.com/a/10725882/18986
Zsh: alias `:e` to `vim`

I sometimes find myself typing this into the command line, so I may as
well make an alias for it.