Add missing case to Type RedHat transformation
Fix CharacterLiteral doc markdown
Remove unused imports
Improve tests (implements + closes #36)

All tests are now toplevel objects (required ceylon/ceylon-sdk#261;
thanks @thradec for implementing it!). This means that tests can access
the test cases (String->Node) of other tests, which reduces duplication.
It also means that we now again have two tests per node type
(previously, we only had one test method), and better yet, they’re
grouped (under the object)!