Parent selector, @path expression, test fixes, better performance

* Support for parent selection via `^`
* Access current path via `@path` in test statements
* multi statement eval
* Performance improvements
  - trace loop redone
    - gathering results recursively
    - expr and path queue are arrays instead of strings now
* fixing travis tests (travis didn't run any tests because travis.yml wasn't configured, meaning `npm test` is used as default -- test script wasn't specified)
* adding in-browser tests

Please note that this PR already includes #15 from @sergi