docs: add a contributing guideline

Let contributors know how to format Pull Requests and what needs to be in issues
chore: add an explicit license file

Some tools look for a license file when auto-scanning. Other people don't know that the package.json file has this info already.

Closes #65
chore: add test tmp dir and npm debug to gitignore
chore: add additional files to npmignore

These files shouldn't be part of the installed package since they are
for development of the package itself
chore: add start of testing to project

This adds tasks and convention to enable testing the task. It also bumps
some dev dependencies.
docs: update README

Adds license info, clearer Markdown formatting and expanded on the
options to make it easier to see defaults, type and descriptions