this change implements the initial v2 experimental api. it is
implemented as an optional series of class that can be configured
through the paste deploy configuration file.
* add wsgi auth validator
* add middleware router
* add v2 endpoints
* add v2 flask blueprint object
* add optional paste filter and composite
* add developer docs for v2 api
Change-Id: I74627c0879851b354b5043f8a6ff91bae8438bb1
Partial-Implements: bp v2-api-experimental-impl