switch to meson build

This is a work in progress effort to modernize our build machinery and use meson, recently adopted by the scipy stack.

In doing this I also follow the approach adopted by the scipy stack of using Tempita, Cython's built-in templating engine.

Rough plan:

• Change the build infrastructure to use meson-python and pyproject.toml
• Implement environment-dependent search for mumps (right now I target conda-forge) Library names can now be passed via a meson build option.
• Figure out the development workflow (running tests etc)
• Update CI
• Explore conda packaging

Also closes #19 (closed) and #11 (closed) (I cleaned up a bunch of code for a good measure).

mumpy/_version.py

+#!/usr/bin/env python
+try:
+    # setuptools_scm is not a runtime dependency. This is used when pip
+    # installing from a git repository.
+    from setuptools_scm import get_version
+
+    __version__ = get_version(root="..", relative_to=__file__)
+except (ImportError, LookupError):
+    from importlib.metadata import version, PackageNotFoundError
+
+    try:
+        __version__ = version("mumpy")
+    except PackageNotFoundError:
+        __version__ = "0.0.0+unknown"
+
+
+if __name__ == "__main__":
+    print(__version__)