allow EARL test manifest to be generated during build

Add Maven profile "test-manifest" so that the manifest can be created
directly from Maven using the command

    mvn install -Ptest-manifest

This is similar to the test-coverage profile we have already.
Merge pull request #108 from spadgett/master

remove debugging statement
Merge pull request #109 from spadgett/manifest-profile

allow EARL test manifest to be generated during build
clarify relative URI resolution tests

Rename some relative URI resolution tests to clarify that they're only
testing the null relative URI, not any relative URIs. These are separate
requirements in the spec. Mark the general relative URI resolution test
as manual (for now at least) since it is not easy to test unless the LDP
server accepts any RDF content.

Fixes #95