Fix for Firefox compatibility

Setting responseType before open() fails on Firefox with:

9 InvalidStateError: An attempt was made to use an object that is not,
or is no longer, usable
Merge pull request #1 from deathcap/httpstatus

Handle HTTP status
Merge pull request #2 from deathcap/fix-firefox

Fix for Firefox compatibility
0.0.2 - publish #1 and #2, add badges
Merge branch 'upstream'