Release 0.4.0?

[yoshiask]

I see that there's a milestone for 0.4.0, but there has not been any activity since 2018. Is there any chance of quickly finishing and releasing 0.4.0? I personally am interested in net20 support, which seems to be slated for 0.4.0 and at least partially implemented in the no_dependencies branch. I'm happy to assist in any way possible.

[yoshiask]

Paging @jnm2 since that no_dependencies branch is theirs

[jnm2]

I was struggling to get test coverage of the code added for net20 support. I'd gladly welcome help, and even forego the tests at this point.