Allow multipart PUT

[vincentjames501]

Haven't looked too much into this, but it looks like you can POST multipart form data, but not PUT it.

Can we just change the Replacement class to accept AbstractContent instead of Content and the put method in Resty to accept AbstractContent instead of Content?

@beders , any feedback? Also, would you mind doing a release for 0.3.3 as we want to rely on the new exception handling (don't throw exceptions on failed responses). Thanks!