virtualenvwrapper plugin cleanup

* removes cd override by using chpwd_functions
* removes subshell call to which by using $+commands array and
  c param expansion to find in PATH
* zsh love!
virtualenv cleanup: replaces subshell with prompt expansion.

* :t parameter expansion returns the last portion of the path,
  equivalent to basename. I <3 zsh.
* adds comments for the VIRTUAL_ENV_DISABLE_PROMPT,
  used by virtual_env activate

See also:
  http://zsh.sourceforge.net/Doc/Release/Expansion.html#Parameter-Expansion
Merge pull request #1878 from spazm/virtualenv-cleanup

virtualenv cleanup: replaces subshell with prompt expansion.
Merge pull request #1877 from spazm/virtualenvwrapper-cleanup

virtualenvwrapper plugin cleanup
Add 'chris' theme
Update zsh prompt
Add custom dir to repo
Remove Climate aliases
Remove spec alias
Add irc alias for weechat-curses
Remove before and after context on grep alias
Add gap alias, remove grep alias
Add custom scripts to repository
Rename scripts to have correct load order
Remove unnecessary init scripts
Change LSCOLORS to better match Thayer color scheme
Move path stuff to oh-my-zsh config
Add node binaries to path
Remove custom LS colors for zsh
Remove custom Square stuff