17 instrumenter

[xentek]

• Adds instrumenter support to hyperdrive, with the interface proposed by @jnunemaker in this blog post: http://www.railstips.org/blog/archives/2013/01/23/an-instrumented-library-in-30-lines/
  • implementation is slightly different but the instrument(name, payload, &optional_block) interface is the same.
• can be configured with the DSL: ruby hyperdrive do instrumenter MyInstrumenter.new end
• the configured instrumenter be called anywhere with hyperdrive.instrument
• can be called inside before callbacks and request handlers with the shorter instrument method, which is just a wrapper around hyperdrive.instrument
• ships with the default Hyperdrive::Instrumenter::Noop class which just returns the given payload (modified by the optional block or not) and a Hyperdrive::Instrumenter::Memory which can be used by library users in tests (and is being used in hyperdrive's own specs).

This pull request does not add any instrumentation to hyperdrive itself, but that is on the road map in the near term.

refs #17

[jnunemaker]

Glad to see the pattern in the wild. I've done it on a few gems and it works great.