Pvmismatch

- fixes issues 11, 12, 13 and 14
- create partial and total crosstied modules
- separate pvcells from pvconstants so that every cell properties can change
- add documentation and testing

Fix setup to install all packages together by creating main project package.
- Renamed `pvmismatch` to `pvmismatch_lib`
- Move all packages inside new `pvmismatch` top level package
- Also move package data and documentation into new top level package
- **Note: Any imports that use `pvmismatch.pvconstants`, `pvmismatch.pvmodule`, `pvmismatch.pvstring` or `pvmismatch.pvsystem` will no longer work.**
- Instead use `from pvmismatch import pvconstants`, `from pvmismatch import pvmodule`, `from pvmismatch import pvstring` or `from pvmismatch import pvsystem`
- For convenience you can use `from pvmismatch import *` to import all four main modules
- Constructors are also exposed to top level package, for example can use `from pvmismatch import PVsystem`

- fix issue with `CalcMPP_IscVocFFeff()` was trying to use dP/dV = 0 to get better estimate of Vmp, but this is at most as accurate as simply using the index found from max(Psys), and probably less accurate, also it was using all Vsys, so it would jump to local extrema
- finally add setup.py and create distribution so users can install