WKT for LAS 1.5

[hobu]

• Point to any OGC CRS WKT definition as valid
• Add Epoch VLR definition
• Entirely remove of GeoTIFF CRS definition

Implements #95 #129

[hobu]

@esilvia I updated this again to try to make it cleaner and simpler to read. I also fixed up the RTD configuration so it renders with every build https://asprs-las--144.org.readthedocs.build/en/144/03_crs.html