add tests/basic-tests.js
add tests/basic-tests.js

- tests: getMarketplaces(), listOrders()
- temporarily tests callEndpoint('GetOrder'), which will likely be the
  next function implemented in mws-advanced :)
- will add more tests as time permits
- tests only that results are not an error condition, and that lists
  have at least 1 element.  Should probably not require 1 element, but
  testing GetOrder with a 0 element ListOrders isn't possible.
- Future should skip tests for which there is no data to supply from
  previous calls (ie, ListOrders returns 0 results, so we can't test
  GetOrder)
- Future should probably test that results are in a particular expected
  format as well, when list length > 0
- Future should be able to save raw results of all API calls and replay
  them back through the tester, so that throttling can be avoided.
- Future should also check for throttling when calling APIs
- Future library work should handle throttling automatically, retrying
  rather than throwing errors.

ericblade/mws-advanced,ericblade/mws-advanced