Added documentation RST files to repo

doc/source/index.rst

doc/source/modules.rst

doc/source/pycgtool.bondset.rst

doc/source/pycgtool.forcefield.rst

doc/source/pycgtool.frame.rst

doc/source/pycgtool.interface.rst

doc/source/pycgtool.mapping.rst

doc/source/pycgtool.parsers.cfg.rst

doc/source/pycgtool.parsers.rst

doc/source/pycgtool.rst

doc/source/pycgtool.util.rst

doc/source/pycgtool.warnings.rst

pycgtool.py

pycgtool/bondset.py

pycgtool/interface.py