Allow SLAssert methods to be called from non SLTest subclass methods
Incorporate PR feedback

Adding a comment to SLTest.h describing when SLAssert should be used
Renaming the static variables to use double underscores
Merge pull request #217 from justinseanmartin/jmartin/allow-asserts-from-non-sltest-subclasses

Allow SLAssert methods to be called from non SLTest subclass methods