pip installable GAM

`pip install` appears to be broken. This used to work after #1417 and #1419:

```sh
pip install git+https://github.com/jay0lee/GAM.git#subdirectory=src
```

It now errors:

```
Building wheel for pyscard (setup.py) ... error
ERROR: Command errored out with exit status 1:
command: /Users/janosh/.venv/py310/bin/python3.10 -u -c 'import io, os, sys, setuptools, tokenize; sys.argv[0] = '"'"'/private/var/folders/5m/sb0wx83j0m36xk_zswkfnffh0000gn/T/pip-install-fsew_zvn/pyscard_03a25dcce2b24efdafc5928d6ab7509a/setup.py'"'"'; __file__='"'"'/private/var/folders/5m/sb0wx83j0m36xk_zswkfnffh0000gn/T/pip-install-fsew_zvn/pyscard_03a25dcce2b24efdafc5928d6ab7509a/setup.py'"'"';f = getattr(tokenize, '"'"'open'"'"', open)(__file__) if os.path.exists(__file__) else io.StringIO('"'"'from setuptools import setup; setup()'"'"');code = f.read().replace('"'"'\r\n'"'"', '"'"'\n'"'"');f.close();exec(compile(code, __file__, '"'"'exec'"'"'))' bdist_wheel -d /private/var/folders/5m/sb0wx83j0m36xk_zswkfnffh0000gn/T/pip-wheel-6v8_svy6
cwd: /private/var/folders/5m/sb0wx83j0m36xk_zswkfnffh0000gn/T/pip-install-fsew_zvn/pyscard_03a25dcce2b24efdafc5928d6ab7509a/
Complete output (8 lines):
running bdist_wheel
running build
running build_py
running build_ext
building 'smartcard.scard._scard' extension
swigging smartcard/scard/scard.i to smartcard/scard/scard_wrap.c
swig -python -outdir smartcard/scard -DPCSCLITE -D__APPLE__ -D__LION__ -o smartcard/scard/scard_wrap.c smartcard/scard/scard.i
error: command 'swig' failed: No such file or directory
----------------------------------------
ERROR: Failed building wheel for pyscard
```

Is a release to PyPI still on the roadmap?