Consider automatically generating the staticdata manifest

[dopplershift]

Right now, adding a new data file requires adding the hash static_data_manifest.txt. There is no need for a human to do this task. We can rely on GitHub's own hashing to handle data integrity, so it should be possible to generate this file during package build.

1. Add new custom build step to setup.py
2. Ensure that built wheels and sdist has the file
3. Verify that editable installs still work

This does mean that the github tarballs aren't sufficient by themselves, but I don't think that's a particularly big deal. Also, editable installs would probably either need to be reinstalled or have the file manually updated when adding a new file, but the latter is the status quo. The benefits here seem to outweigh the downsides.