Request: Support Python's requirements.txt

`requirements.txt` is typically located in the root of an application. The file format is [documented here](https://pip.pypa.io/en/stable/reference/pip_install/#requirements-file-format).

Examples:
- [scrapy](https://github.com/scrapy/scrapy/blob/master/requirements.txt)
- [boto](https://github.com/boto/boto/blob/develop/requirements.txt)
- [PokemonGo-Bot](https://github.com/PokemonGoF/PokemonGo-Bot/blob/master/requirements.txt)
- [requests](https://github.com/kennethreitz/requests/blob/master/requirements.txt)

`requirements.txt` may point to other requirements files like [this example](https://github.com/fabric/fabric/blob/master/requirements.txt).