Move to single python package "hsp2"

[timcera]

• Moved the HSP2, HSP2IO, and HSP2tools top level packages to hsp2.hsp2, hsp2.hsp2io, and hsp2.hsp2tools respectively.
• Corrected the imports in python and Jupyter notebooks to use the new locations.
• HSP2 can be run in all of the CompareHSP2.ipynb in tests/, however some do not have the HSPF results to compare to.
• The Jupyter notebooks in examples/ need some work to find input data and where to write output.