relative selectors

## summary 

- [x] separated into small modules for testing purposes
- [x] tape tests
- [x] made the API spec-compliant
- [x] separated `Document` `DocumentFragment` method from `Element` ones (scope don't make sense there) 
- [x] used a stronger feature-test for `query` presence
- [x] gulp + browserify + jshint
- [x] prevented conflicts between concurrent versions
- [x] `pushUniq` optimisation using element property setting and `map` to prevent loops used in `indexOf`
- [ ] to cross when fucking testling works :smile: 

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