Register additional serializer plugins for SPARQL mime types.

[darrengarvey]

This mirrors the similar parser registrations below in the same file.
With this commit, an Accept header can be used directly to serialize a
response, making putting up a SPARQL compatible endpoint trivial.

[coveralls]

Coverage increased (+0.006%) to 75.894% when pulling 09d0652 on darrengarvey:register-additional-mimetype into 2aebbf0 on RDFLib:master.

[ashleysommer]

@darrengarvey
This looks great, thanks.

Just one thing we'd like to discuss before merging.

Do we really need two different entries for application/sparql-results+xml; charset=UTF-8 and application/sparql-results+xml? Seems this is an opportunity to make this lookup more concise.

I understand the content-type header can and sometimes does include the charset (or other additional parameters), do you expect the user will pass that directly into the serializer? Should there be a mimetype sanitizer that splits removes anything after a semicolon when matching the mimetype to serializer (or parser)?

[darrengarvey]

I was following the pattern from a few lines below on the parser side, which was added intentionally in #941.

Actually the charset isn't valid in the Accept header: there is Accept-Charset for that. The line you referenced was redundant, so I've removed it. Thanks @ashleysommer!

[ashleysommer]

Thanks. Merged, just in time for the 5.0.0 release.