Cleaned up nanmad -> mad issues
Revert "Cleaned up nanmad -> mad issues"

This reverts commit fe10bc62af58af66ce4dd185fee8add7246c6852.
Cleaned up the nanmad -> mad consequences
Fixed up scale test to match the new SpectralCube API
More tests; cleaned up estimate methods.
added signal masking option to the estimate_noise method.
Monkeying with docstrings.
Merge pull request #18 from low-sky/master

Cleanup and testing of AKL changes.