ingest custom matcher json or yaml

[halorium]

This is a proposal to modify http-spec so that matchers are not built-in but rather loaded via json or yaml files.
Just like the htsf files are copied to the docker container as well as the run-http-specs file.
matchers.yaml could be handled if provided
a matchers.yaml could be loaded for the built in matchers as well
This will allow custom matchers to be added very easily without modifying the code.

[halorium]

A solution is provided in #41