= docs: extract signature lines with `includecode`

by matching `def <snippet>` up to (but not including) the trailing `=`
= docs: document `headerValueByName` as an example for documenting other directives
= build: update to sbt 0.12.4-RC3

Performance of (cold) sbt compilation for Scala != 2.9.2 was slow. This
should improve the speed of travis builds.

See
https://groups.google.com/forum/#!topic/simple-build-tool/HMjm3jpHc6Y
Merge pull request #341 from spray/feature/document-directives-stub

Directive documentation example
Merge pull request #343 from jrudolph/wip/upgrade-to-sbt-0.12.3-RC3

= build: update to sbt 0.12.4-RC3
! testkit: small clean-up, remove duplication with httpx RequestBuilding

This change removes the `pimpHttpRequestWithTildeArrow` method from the RouteTest trait
and brings the previously `private` TildeArrow class and object into scope. The latter
allows for explicit (manual) provision of `~>` implicits in order to simplify diagnosis of
implicits resolution issues.
Merge remote-tracking branch 'upstream/master'
Issue 9: Adding Coda Hale metrics to Spray

- Fixed a couple of spelling mistakes in comments.
- Changes the HTTP method on auto-generated metric names to be at the end of the
  name instead of the start
- Factored out some common code into MetricHelpers