Update README.me with known bugs section

Reword help menu descriptions of positional arguments

Remove unnecessary top-level import

Update command-line usage of dph/pohlig.py to match dph/__main__.py

Move common utility functions to dph/util.py

Fix bug where incorrect solution is found for large exponents

Update usage instructions in README.md

Move dph.py to dph/__main__.py

Swap order of positional arguments passed to 'exp' subcommand

Remove multiplication operation with unused result

Update README.md with requirements and usage descriptions

Add .gitignore file

Add pip/pipenv depedency management files

Add initial code for Python DPH module and command-line utility

Add README.md and LICENSE files