MiniRUM js. Lightweight implementation of RUM.

[chicharr]

Principles:

• much smaller than the current sampleRUM 50% reduction in size minimum, 75% would be good, 90% optimal
• aggressively drop checkpoints that are no longer insightful
• make embedding it into an existing codebase (boilerplate or other) easier, ideally just one required line to get started
• push more functionality into helix-rum-enhancer, basically everything that is not required for page view counting
• (possibly) drop functionality like on, always.on, defer, etc. that's too clever for our own good