Nhse o40 orkv.i141 silvermachine

[martinsumner]

Switch HTTP API to use SilverMachine not WebMachine/Mochiweb.

Intentions are:

• improve performance of common requests, especially with significant volumes of index entries and/or user object metadata;
• simplify the callbacks required within the application;
• only implement the basics of HTTP, the full extent of rules (i.e. equivalent webmachine decision_core) may be implemented in the callbacks, but aren't applied by default;
• allow for streaming on both inbound request bodies as well as outbound response bodies, to ready support for file upload/downloads;
• simplify the task of providing SSL handshake information to the application

[hmmr]

Overall, designing this riak component as a pared-down http server, with no attempt to present it as a general purpose http server outside of riak, is clearly the right approach. A handful of non-critical issues; otherwise, ready to approve.