In order for the package to be installable via git (and to remove dist
from git), then the `prepare` script will need to be runnable from the
user's machine. Which means `yarn` needs to be available to npm users.

Whitelist files rather than dealing with npmignore override of
gitignore.

Package now includes src, lib, dist, and TS typings. (package.json,
readme, changelog, license are included automatically by npm)

Things no longer included in package: regression, test, examples, docs

Browserify won't create necessary directories. So they need to be
created prior to running the builds. Which also means we need to use a
cross-platform `mkdir` command. And we need to run the clean command as
part of build/preparation so we need cross-platform rm-rf.

Unsure how best to "advertise" the dist download. Custom badge for now.

Link points to dist/ dir at latest published version.