Fixed problems with wrong EARL term names (wrong in openrdf.org vocab)

Converted some manual tests to client-only, since they were that.

Fixed #92
Wrongly skipping slug test and should pass patch test if server doesn't support
Moved client-only tests out into separate RDF manifest.

Closes #126
Merge pull request #124 from spadgett/master

add link to test documentation from EARL manifest
Put manual tests into their own group, this will help those who want
to run the test suite repeatedly to not have to have clutter of manual skipped
results.
don't override JSON-LD context for EARL reports

The JSON-LD library generates a better context than the one we are
using.