Add references to the antigen and prezto ZSH frameworks.
Add antigen-hs to ZSH frameworks
Add dotzsh reference
Merge remote-tracking branch 'upstream/source' into add-antigen-reference

Conflicts:
	content/index.md
Merge pull request #51 from unixorn/add-antigen-reference

Add references to the antigen, antigen-hs, dotzsh and prezto ZSH frameworks. Closes #29.