Add Data option to push. 

* bump to v.1.5
* Since dev changed significantly, had to refactor #88 into this version

@kitcambridge r?
Huh, looking at http://golang.org/src/pkg/net/http/request.go?s=22373:22408#L695, I think we're covered. It's using limtReader and is limiting to 10MB. Plus, if we use the built in, we don't have to reimplement the content type handling. If we have a data chunk smaller than 10MB, we obviously lose some efficiency by over-reading, but I think it's reasonably acceptable.