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).

pyproject.toml

@@ -2,7 +2,9 @@
 requires = [
     "cython >= 3.0.2",
     "meson >= 1.0.0",
-    "meson-python >= 0.14.0",
+    "meson-python >= 0.15.0",
+    "numpy==1.24.4; python_version=='3.11' and platform_python_implementation != 'PyPy'",
+
 ]
 build-backend = "mesonpy"