Cmf

- Compiles on MacOS again (57)
- Safe and downcasted item retrieval from solver states (53)
- New ET method (OudinET, 34)
- Added number of tolerable solver errors (56)
- Fixed ImplicitEuler (58)
- Fixed usage of scalars for retentioncurve functions (60)

cmf 1.4 is mainly a bug / documentation fix release, with mild enhancments.
Major enhancment is the bracket access for solutes, however, not all tutorials / demos are already updated.

Fixed issues:

Bugs and inconsistent equations
- 46 pip install cmf fails for linux / mac os
- 37 Shuttleworth-Wallace: Inconsistent behavior in wet to dry leaves transition
- 38 Surfacewater: Inconsistent methods to calculate covered area

Enhancements:
- 31 More crossection types can be implemented on demand
- 29 Bracket access to solute storage
- 50 New connection names are already available as alias

Documentation
- 45 Technical Flux and Waterbalance Tutorials need reworking
- 30 Error API Manning equation
- 35 GIR of ShuttleworthWallace description

The documentation is moved to GitHub and tutorial and API documentation are tied together. All Python code is now Python 3 compatible and Appveyor is used to produce binary distributions of cmf for Windows. cmf.draw is modernized and better documented. Other obsolete and undocumented extra packages have been removed from the source.

A new approach for dealing with Geometry in cmf using saved geometry data in cells. Handled MacOS problems and fixed a regression from v1.1.1

- Fixed 6
- Worked towards geometry holder for cells in 8.