Add project jump module

Port of project-jump `pj` from oh-my-zsh. 

Couple things:
 * The docs at the moment say to set PROJECT_PATH env var in .zshrc. Should I change this to say .zprofile instead?
 * pj function seemed too small to put into it's own folder. Let me know what is best here. Thanks



#### Basic Usage
  - Set `$PROJECT_PATHS` in your ~/.zshrc
    e.g.: PROJECT_PATHS=(~/src ~/work)
  - In ZSH you now can open a project directory with the command: `pj my-project`
    the plugin will locate the `my-project` directory in one of the $PROJECT_PATHS. Also tab completion is supported.
  - `pjo my-project` will open the directory in $EDITOR