Completed first pass on ES6 Promises tests: Promise static api tests

# High points:

1. removed the direct coupling to 'npo'.
2. copied the 'adapter' model used in promises-aplus-tests ; tests will work with both native Promises and a polyfill
3. flattened test hierarchy per @domenic 's suggestion https://github.com/getify/native-promise-only/issues/14#issuecomment-45416751
4. Wrote all the tests I could, translating spec into user-land javascript

# Low points:

1. of about 80 specs, 29 are still 'pending' because I am not sure how to translate them into code, or even *if* they can be translated into code since some are constrains on internal behavior of the Promise object that I cannot access to verify
2. 6 tests are failing.  This probably due to (in decreasing order of likelihood)

     a. my incorrect reading of the spec
     b. my incorrect implementation of a test
     c. using the older version of npo (my net access was down for ~12 hrs yesterday, so I didn't get your updated version)
     d. a bug in npo
     e. a bug/ambiguity in the spec

# To run:

 To run the ES6 promises suite and the promises-aplus-tests and get coverage reports, do `npm run-script cover`

 To just run the ES6 promises suite, do `test/cli.js test_adapter.js --grep 25.4`

25.4 is the section of the ES6 spec that deals with the implementation of promises.

Comments/suggestions very welcome.