Provide a method for generating a method from a range instead of a selection #85

[palenshus]

It would be convenient to be able to generate a frament from a range directly, instead of having to go through a Selection. It'd be a simple refactoring, and would make the library more flexible. I'm thinking something like:

const generateFragmentFromRange = (range, startTime = Date.now()) => { ...

[erickjth]

This PR #152 should fix this.