2.0.0

Features:

Python Wheels: Wheels are supported for linux including manylinux1, manylinux2010, manylinux2014
Nixpkgs python packages: Nixpkgs is now treated as a separate provider. That means packages can be taken directly from there, independent on their availability from pypi.
Configurable Providers: The user can now freely decide where packages should be taken from either via a default or on a per package basis. Currently available provider are nixpkgs, sdist, wheel.
Core architecture - Python Overrides: The core of mach nix now produces python overrides instead of nixpkgs overlays which makes it much more composible and allows for a less strange API.
Overlay support: mkPython and lower level interfaces now accept new parameter pkgs and python which indirectly enables you to use any nixpkgs overlays (But don't use this for modifying python packages. Better do this with Python Overrides)
Python Overrides support: mkPython now accepts new parameter overrides_pre and overrides_post each allowing to inject a list of python overrides to apply before and after the mach-nix internal overrides. This allows you to fixup packages or add your own modifications to them.
Extras support: All providers now fully support python extras. That means requirements like for example 'requests[security]' will be correctly resolved.

Removed:
- mkPythonExpr: removed in favor of machNixFile and machNix
Added:
- machNixFile which generates a nex expresison
- machNix which evaluates the generated nix expression to get overrides and select_pkgs
Changed:
- mkPython:
  - Removed arguments:
    - python_attr in favor if python
    - prefer_nixpkgs in favor of providers
    - nixpkgs_commit in favor of pkgs
    - nixpkgs_tarball_sha256 in favor of pkgs
  - Added arguments:
    - overrides_pre: list of python overrides to apply before the machnix overrides
    - overrides_post: list of python overrides to apply after the machnix overrides
    - pkgs: pass custom nixpkgs. Only used for manylinux wheel dependencies.
    - providers: define provider preferences
    - _provider_defaults: builtin provider defaults. Disable them by passing {}