extract histograph specific namespaces to config file

[tomdemeyer]

extract histograph specific namespaces to config file
.. and allow other namespace configs

[bertspaan]

Yes!

[wires]

or maybe even consider turning the uri-normalizer into a github organization and have on repository for each URL namespace. URIfiy the WORLD 🎉

only the URN namespace urn:hgid is histograph specific, urn:hg just means uri-normalizer understands that URN <=> URL mapping and can do it's URI normalizing thing