Add spectral_cube sub-package
Add API docs for utils.testing
Move spectrum.diffuse.GalacticDiffuse to
spectral_cube.core.GammaSpectralCube
Add datasets.get_fermi_diffuse_background_model
Add examples/fermi_diffuse.py
Add LogEnergyAxis class
Implement GammaSpectralCube class
Add datasets file: gll_iem_v02_cutout.fits
Add access function to fermi diffue model cube
Continue GammaSpectrumCube implementation
Fix bug in LogEnergyAxis
Bug fixes and more tests for GammaSpectralCube
Merge pull request #118 from cdeil/spectral_cube

Add spectral_cube sub-package