Don't attempt to save 'arguments' metadata for classes

See #41
Introduce import_method() to import method data

An attempt was being made to add some method metadata to the class,
which was causing undefined index notices. This moves that out into the
new `import_method()` method.

Fixes #41
Formerly: #62 (importing hooks within methods; may be closed)
Import more class data

We export ‘extends’, ‘implements’, and ‘properties’, but we weren’t
importing them.
Merge pull request #64 from JDGrimes/issue-41

Don't attempt to save 'arguments' metadata for classes