base.py exposes protected attributes

[jonathan-benn]

In base.py, there are several entities (attributes, methods, classes), including the following:

Pure
wrap2spy
unwrap
wrap2stub
args_type
pure
obj
prop
orig_func

These entities should probably be renamed to add a _ prefix (protected), to discourage end-users from trying to use them. The entities should be protected because they are used in child classes like SinonSpy and SinonStub.