Add regexp support to the message matcher

- Move the Matcher out of the pipeline package to message
- Rename FilterSpecification to MatcherSpecification
Fix the aggregate output in CounterFilter

The interval can exceed the test condition when there is no input
causing the aggregate to never be flushed again
Merge branch 'dev' into features/message_matcher

Conflicts:
	pipeline/all_specs_test.go
Merge pull request #43 from mozilla-services/features/message_matcher

Features/message matcher
Add benchmark tests (this is just the start)

- Addressed a few performance issues with access to the Message
Fields
- Updated the read_message API to take the field and array indices
as parameters instead of embedding it in the string (saves parsing
and conversion)
Merge pull request #46 from mozilla-services/features/benchmark

Add benchmark tests (this is just the start)
Merge branch 'dev' into features/handoff-pipeline

Conflicts:
	pipeline/config.go
	pipeline/filters.go
	pipeline/router.go