Documentation update

[earth-chris]

This PR will create the baseline package documentation to showcase the features of earthlib. This will primarily be a series of notebooks, some markdown updates, and a cleanup of the development environment.

[earth-chris]

The changes to the spectral library included:

• Removing a few NPV spectra with bad ASD measurements from the very spiky measurements at a couple of wavelengths (removed only from the optimized library)
• Restructuring the L3/L4 definitions to keep L4 as measured/modeled, since the L2/L3 hierarchy was a little clearer (lc type to lc sub-type)
• Reorganized the library to use the optimized library by default, then exposed the full reference spectra via the full_library instance