Should require "pathname" for dir2ro script.
Fix up the provenance documentation comments.

Most refer to either ROs or Manifests when they should talk about resources as
this is a mixin that provides fields at different levels - not just the top
level RO.
Add missing provenance tests.

Need to check that timestamps are Time objects and agents are Agent objects
after being set by a string.
Add retrievedOn field to the provenance.
Add retrievedBy field to the provenance.
Add retrievedFrom field to the provenance.
Annotations now use "uri" instead of "annotation".

For their identifiers.
Aggregates now use "uri" for both files and URIs.
Add test-unit gem to the dependencies.

Ruby 2.2 requires this to be added explicitly.
Tidy up the gemspec file.
Update the RO spec and homepage URIs in the gemspec.
Cache the gems used in the tests in Travis.
Fixup the documentation of Aggregate#mediatype.

Needed tweaking after the removal of the distinction between file and URI
aggregates.
Add support for ORE Proxies to Aggregates.

Simple read-only support at this stage.
Merge branch 'rh/new-travis' into next

* rh/new-travis:
  Cache the gems used in the tests in Travis.
Make sure Provenance#retrieved_from= uses Strings.

Not URI objects.
Document the Provenance#retrieved_from(=) methods.
Use a new base class for manifest entries.

This will help with tracking edits and the addition of provenance fields.
Wire up the edited? methods for manifest entries.
Allow direct editing of aggregates via the manifest.