Finish up documentation.

doc/geometric-algebra.rst

doc/index.rst

doc/mappers.rst

doc/misc.rst

doc/primitives.rst

pymbolic/__init__.py

pymbolic/algorithm.py

pymbolic/geometric_algebra.py

pymbolic/mapper/__init__.py

pymbolic/mapper/c_code.py

pymbolic/mapper/collector.py

pymbolic/mapper/constant_folder.py

pymbolic/mapper/dependency.py

pymbolic/mapper/differentiator.py

pymbolic/mapper/evaluator.py

pymbolic/mapper/expander.py

pymbolic/mapper/stringifier.py

pymbolic/primitives.py

setup.py