Update release workflow to build source and binary distributions

[mattt]

Resolves #81

The current release workflow builds the Python package for distribution using the following command:

python -m build --sdist --outdir dist .

Looking at the help text for the command, the default behavior is to build both source and binary distribution. By specifying --sdist, we're opting out of a binary distribution, so we can remove it to opt back into that behavior.

Going a step further, the default options use dist as an output directory, use the current directory as the source directory, and build source and binary distribution, which is what we're already doing. So we can get the desired behavior by running without any additional options:

python -m build

[mattt]

@bfirsh Any reason not to package a binary distribution alongside the source? When I ran this locally, the resulting filename had the suffix -py3-none-any.whl, which seems to indicate compatibility with any version of Python 3 running on any platform.