Plugin manager

Plugin manager for the new plugin structure

 - Install
  - From Rubygems
    - Latest
     - Specific version
  - From gem file

 - List installed plugins
   - All
   - Specific name
   - Specific group

 - Uninstall a plugin

 - Update
   - Single plugin to latest version
   - Single plugin to specific version
   - All to latest version
hehe, indeed. After much deliberation, @colinsurprenant and I agreed that explicit return can be avoided in most cases.

However, if your method intends to return nothing, you must have 'nil' be either implicitly or explicitly returned from your method.