Backends: Add simple read-only backend for testing.
Backends: Use helpers to simplify tests.
Query: First draft of graphite-compatible query engine.

The parser is built using the Ragel parser-generator, so that will be
needed in case any changes has to be made to the actual parser.
Makefile: gofmt ragel output.
Parser test: Build better example data.
Parser: Remove the initial toy parser.