Set Content-Length header for multipart requests (including a test). Fixes #64.
Make multipart.sizeOf work with numeric values
Set Content-Length for multipart requests
Test for Content-Length header in multipart requests
This also includes #77, I thought it was a separate issue but then I added a test for the issue in #77 when I made the test here, so they're dependent after all.
It definitely fixed my issue uploading to Scribd.