The development workflow can be used with Node 4+, not just Node 6. We
should avoid showing warnings and errors when users are installing this
package via npm/yarn.

Ref. #1729, #1743.
Closes #1725.

Bump node engine in packages.json

more in-depth documentation of slide backgrounds #1542

Simplify full setup

`./*.md` didn't work `*.md` does work

Fixes #1549, now UA match is limiting out MS Edge and Chrome detection is improved. Also improved UserAgent access by storing it in to a local variable, it was accessed so many times in different places.

readme tweaks

Table of contents added in README.md