Fix freeze tests.

The tests for jsnx.freeze and jsnx.is_frozen didn't run. Also fixes the
implementation of those functions.
Fix exports part 3.
Fix edge label positioning
Add 'jsnx.version' and sets the version to 0.1.

The current version serves only as a reference point and has no
particular meaning.
The goal is to release version 1.0 when the library is fully ported.