Update install.zsh, add pathogen.vim submodule.

Add:
	install.zsh
		-Compartmentalize different setup steps with functions
		(eg, `create_regular_links()`, `create_symbolic_link()`)

Fix:
	install.zsh, vim/bundle/pathogen/
		-The lack of plugin functionality and proper color on remote machines
		stemmed from the fact that my Vim plugins rely on `pathogen.vim` for
		detection and sourcing, and the `pathogen` plugin was never added as a
		`.dotfiles` submodule (nor properly linked with ~/.vim/autoload).