Uw add build hooks (+ prep for release)

This PR prepares for a release tag, and contains the following:

* All deps are tagged (except jiffy - yet - since it has none)
* The `folsom` dep re-targeted to Basho's version
* Remove exometer_report_riak.erl
* Add hooks for custom-processing of the rebar.config (documented in the README.md)
* Rebuilt documentation

Any objections should be raised quickly; will merge soon.
You could at least use the latest commit in master, so you actually have a sticky reference.