Compile on 2.11, introduce settings for dependency versions.

Bump version and make it a snap!shot to 0.4.3-SNAPSHOT.
(Build's version should end in -SNAPSHOT for nightly).

Depend on parser combinators for tests.
Rework Arbitrary instance for Enumeration.
Enable Travis CI

Update to ensure we have latest scala SNAPSHOT
Allow snapshot build to fail for now.
Will need some machinery as in scala-xml build to determine
binary version when compiling with Scala -SNAPSHOT