FastDSS, Oddie and AltDSS C-API 0.15.0

[PMeira]

This PR adds relevant code to support the new features:

• FastDSS backend: new CPython backend written directly in C. The CFFI backend is still used for many features.
• Oddie support: Oddie, originally for "OpenDSSDirect.DLL Interface Extender", allows loading EPRI's OpenDSS and OpenDSS-C through their modern DCSL approach. OpenDSS-C is the newish C++ implementation from EPRI and works on Linux too.
• AltDSS C-API 0.15.0: currently in beta, merges a lot of changes except some API and backwards compatibility changes (which will be included in a future release).

TODO:

• Check and update docs
• Reenable AltDSS-Python as optional dependency (disabled for testing, since it has not been released).
• Wait upstream packages to be released

Notable changes (more will be listed in the changelog or release notes):

• Some changes in the engine, mirroring some of EPRI's changes, can result in numerical differences. For example, the line model had some updates, so many circuits that use LineGeometry and similar constructs might result in slightly different results.
• We now default to using NumPy arrays for many functions. This can now be easily toggled though.
• Stricter data model by default. This avoids many errors. It can also be easily toggled.

[PMeira]

First beta release at: https://pypi.org/project/opendssdirect.py/0.10.0b1/

Working on preparing a release for AltDSS-Python later today.

[PMeira]

• https://pypi.org/project/opendssdirect.py/0.10.0b2/
• https://pypi.org/project/altdss/0.3.0b2/