Duckargs

* Fix issues that cause broken python/C programs to be generated when language keywords are used as option names (e.g. "duckargs -i --int")
* Ensure that NULL pointers are not passed to printf in generated C code
* Fix unnecessary trailing "optind++" in generated C code
* Minor improvements in "usage" printout in generated C code

**Full Changelog**: https://github.com/eriknyquist/duckargs/compare/v1.4.0...v1.5.0

* Add support for generating C code

**Full Changelog**: https://github.com/eriknyquist/duckargs/compare/v1.3.0...v1.4.0

* Add CLI script to setup.py, so 'duckargs' can be called directly (i.e. 'duckargs' instead of 'python -m duckargs')
* Populate ArgumentParser 'description' field in generated programs
* Recognize hex values and negative values as ints
* Fix bugs when positional arg is a float/int
* Add DUCKARGS_COMMENT and DUCKARGS_PRINT environment variables

**Full Changelog**: https://github.com/eriknyquist/duckargs/compare/v1.2.0...v1.3.0

* Improve filename handling a bit (add FILE option argument)
* Add usage printout on empty args

**Full Changelog**: https://github.com/eriknyquist/duckargs/compare/v1.1.0...v1.2.0