more cleanup and groundwork

Quite something, but only internal organization. Major points are:
- lodash 1.0.0 came out yesterday and I'm using it, so plz `npm update`
- split up things, eg new `util.js`
- more tests, particularly for `test-helper` itself (!)
- new assertions `isPlainObjectOrFunc` and `isProperSubset` (for our own tests); + some tests for *them* too, but these are incomplete - it's getting time now for https://github.com/busterjs/referee-combinators/issues/5 , "Don't rely on AssertionError from failure"