Backends: Document helper functions.
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.
Query: Use new backends-helpers.
Query: move things around a bit.