Split NewRequest() and DoReq() out of APIReq().

This will allow the caller to make changes to the API request (such as
adding headers where appropriate).
Use new v3 log-sessions API. Fixes #73.

Also remove Acceptor interface and url.Values option, they are no longer used.

Because of removed Acceptor interface, NewRequest no longer requires v.
Rename tail -p to -d to be consistent w/ 'dyno' noun