ZSH: Add decent .zshrc

From thoughtbot, striped and adjusted with some own stuff
VIM: Add syntastic, ctags bundles + new settings

- Add syntastic bundle
- Add ctags bundle
- Add new settings for ctrlp to use ag (silver searcher) instead of
	grep, when possible
- Some .vimrc finetuning and new shortcut for switching between the
	two last files