Package handler

The amplee.atompub package is the heart of amplee has it carries
the mapping of APP entities. However that package does not
mention HTTP anywhere. The amplee.handler package is meant to deal with
that aspect of APP.

Basically amplee.handler defines:

 - a class MemberHandler that can be called to perform operations
   on an amplee.atompub.store, collections and members.
 - a class MemberType to inform how the MemberHandler class should
   handle resources based on their mime-types
 - Two sub-packages allowing an easy integration of a store within
   a CherryPy or WSGI application.

Most of the time MemberHandler will not need to be handled directly
by the developer who will prefer the higher level interface provided
by the CherryPy and WSGI handlers.