Prefix V2 APIs with /api

The mail thread
http://lucene.472066.n3.nabble.com/v2-API-will-there-ever-be-a-v3-td4340901.html

it makes sense to prefix v2 APIs at /api intsead of /v2 if we never plan to have a /v3

In principle, it makes total sense
The challenge is that it takes a while to change the code and tests to make to work. Should this be a blocker and should we hold up the release