Dynamically load requirements.txt in pyproject.toml

[jepler]

This allows use of pip install -r requirements.txt by users who prefer that way of trying out the package, while not affecting my typical usage.

This does create a dependency on a beta feature of setuptools, so it could be fragile.

Closes: #5

[jepler]

@peterkaminski does this meet your needs? do you know anything more about why setuptools says this feature is "beta"?

[peterkaminski]

@jepler yes, this is great. Thank you!

I don't have specific knowledge about why the feature is beta, but after some reading, it seems to be that it's "beta" because the maintainers wanted to see if they would get feedback about the naming of the directive, how it operated, etc.

There was also some consternation about the feature itself (if I'm reading correctly), but it also looks like they've decided to proceed with the feature anyway.

Here are the links I read:

• Add beta status to 'file' directive for reading dependencies · pypa/setuptools@645a53f
• Allow file: for requires statements in setup.cfg by akx · Pull Request #3253 · pypa/setuptools
• Allow file: for requires statements in setup.cfg by akx · Pull Request #3253 · pypa/setuptools (see especially the comments from abravalheri and pganssle on Jun 19, 2022)
• Allow file: for dependencies in TOML by akx · Pull Request #3255 · pypa/setuptools (not sure if this is relevant)
• Allow file: for dependencies in TOML by akx · Pull Request #3255 · pypa/setuptools (the code change itself, not directly relevant because there's no discussion here, but it might be a way to find more information)

[jepler]

I also added an (arguably terrible) top level chap.py script, to allow running python -mchap or ./chap.py in the top level directory, after installing requirements with pip install -r requirements.txt.