Also include bootstrap.js to make collapsing actually work, and change
order of links in head to ensure js is included in the 'correct' order

This is still pretty quick and dirty, with lots of refactoring and
general tidying up ahead; but it gives an example structure to start
from

Emphasis on the dirty, not so much 'quick' ! This shows select outputs
from the default Asphodice class:
 - rerolls
 - outcome balance
 - outcomes

This information is presented in a Bootstrap card:

https://getbootstrap.com/docs/5.0/components/card/

Can now build all with 'gulp' (if gulp-cli installed)

Big commit. Breakdown:
 - .gitignore includes gulpfile.js (otehrwise excluded)
 - gulpfile sets up build steps + browsersync
 - src/ files for FE (stub for now)
 - moved ts to src/ for consistency
 - update tsconfig with new paths
 - package.json lists new reqs