Function for converting Python values to an explicit Java type

Fix a bug in cast
Add an as_jobj method to convert a Python value to a Java object of the given type. This leverages the existing JPy_AsJObjectWithType method.
Update some tests to match current behavior (e.g. returning Byte instead of Integer)
More logging during tests
Fixed failing hashNegativeOne test
Replace incorrect return Py_NONEs with Py_RETURN_NONE (for correct reference counting)

jpy-consortium / jpy