CCBC-427: Add common HTTP parsing functionality

This provides a wrapper around http_parser which performs its own
internal buffering. This will be used to replace the ad-hoc
implementations currently found in the views and bc_http.c code.

Tests are provided as well.

Change-Id: I76ee952accb8493ea51dd80f471ca96e0ed23c85
Reviewed-on: http://review.couchbase.org/37571
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>