A new script to make creating new Beman libraries from exemplar easier

beman.exemplar now has a new stamp.sh script, and instructions in the README for how to use it to create a new Beman library:

Previously, users needing to create a new Beman library properly would
need to follow the following set of (undocumented) instructions:

  • Go to the ‘exemplar’ repo, click ‘use this template,’ click ‘create a new repository’
  • create and checkout the new repository
  • cd cookiecutter
  • python3 -m pip install cookiecutter
  • cookiecutter .
  • Go through the prompts to populate the template
  • Copy the resulting directory somewhere outside of your repo
  • Blow away all the files in the repo (careful to include hidden files like .github while still including .git) and replace them with the contents of the directory that cookiecutter produced

The new stamp.sh script now automates all but the first two above
steps, and the new instructions in the README.md explain to users how
to use it.