Allows for more expressive code when constructing help messages for cells.
Will also move extra logic in parsing help strings into the initial python parse instead of doing it in the C++ at export time.
* `misc/__init__.py`:
* checks if there's a `yosys-abc` in the same directory - if yes, sets the variable `sys._pyosys_abc`
* checks if there's a `share` in the same directory - if yes, sets the variable `sys._pyosys_share_dirname`
* `yosys.cc::init_share_dirname`: check for `sys._pyosys_share_dirname`, use it at the highest priority if Python is enabled
* `yosys.cc::init_abc_executable_name`: check for `sys._pyosys_abc`, use it at at the highest priority if Python is enabled
* `Makefile`: add new target, `share`, to only create the extra targets
* `setup.py`: compile libyosys.so, yosys-abc and share, and copy them all as part of the pyosys build
* `test/arch/ecp5/add_sub.py`: ported `add_sub.ys` to Python to act as a test for the share directory and abc with Python wheels, used in CI
* Created `setup.py`: Python package manifest to build `pyosys` wheels with a custom extension to build and include `libyosys.so` using Make
* `.gitignore`: Added byproducts of the Python wheel build process
* `Makefile`: Added `-undefined dynamic_lookup` to `libyosys.so` so missing symbols can be resolved by importing into a Python interpreter
* `kernel/yosys.cc`: Gated `PyImport_AppendInittab` with `!Py_IsInitialized`; as of Python 3.12, the interpreter is already initialized and `PyImport_AppendInittab` would cause an exception to be raised
* Created `wheels.yml`: CI workflow for building wheels for CPython on:
* Linux (glibc, musl) and Darwin
* x86-64 and arm64
* Less brittle method of adding script dirname to sys.path
* Check if scriptfp successfully opens before using it
* Move `log_error` to after `PyErr_Print()` is called
