Better streams

This removes the buggy `multipart-stream` library and uses the new `request` library capabilities to upload streams. Uploading a 3GB file on old implementation would cause node to immediately allocate 3GB of memory. Now Node consumes memory as it uses it. In my tests with the 3GB file, the memory usage did not exceed 100MB.

Fixes #327 
Fixes #236 

@rakyll can you review?