Moving all zsh config options into a lib/ subdirectory to make way for some upcoming changes to directory structure and configuration options

`git-symbolic-ref` needs to be `git symbolic-ref`

 * Improved speed, the first time cd'ing into a git repo the prompt
   returns much faster (for me at least).
 * Prompt is now decorated in nested folders within a git repo. No
   longer check for the '.git' folder.

 * git.zsh is now themable:
   * git_prompt_info() now will look in the following variables for
     formatting strings:
     * ZSH_THEME_GIT_PROMPT_PREFIX - Prefix for the prompt (before the
       branch name)
     * ZSH_THEME_GIT_PROMPT_SUFFIX - The very end of the prompt
     * ZSH_THEME_GIT_PROMPT_DIRTY - Displayed when the branch is dirty
     * ZSH_THEME_GIT_PROMPT_CLEAN - Displayed when the branch is clean
 * Updated geoffgarside, robbyrussell, and maran to work with new git
   theme
 * Added the Risto theme, which is very similar to a number of bash
   prompts, and allows me to use zsh in with out my co-workers knowing I
   have the advantage. Think of it as a ninja theme.

Updating the name of the rake and capistrano task cache file to append a ~ to the end of the filename so it's easier to ignore in rails git projects. [#1]

Updating install process to copy your current environments PATH and adding it to the bottom of ~/.zshrc.