Merge pull request #22 from plmday/master

Missing lambda-cube instances added
First working parser test.

Is there Eq for terms? I am currently comparing the textual representations of a parsed and pretty
printed text and the expected pretty printed AST.
Copy remaining pretty printer tests to parser tests.
More parser tests.
Copy new parser tests to pretty printer tests.
Merge pull request #24 from morphling/parser-tests

Add parser tests (fix #16)
Avoid name clashes by commenting out some code (#27).
Resolved name clash