Fill in missing API info, put todo to verify MD5 hash of uploaded file

I too had to reverse engineer the puush.me upload api to implement an open source client to use with linux.  Together with this project, we can have an entirely open source puush-like software stack. :)

This pull request just fills in the missing parts of the API, and puts a todo with regard to verifying that the uploaded file's MD5 checksum matches what is expected.  If you would like me to write and put in a pull request for the MD5 verification code myself I can do that as well.

I refrained from linking to [my client](https://github.com/moparisthebest/open-screeny) in the readme as it seemed like shameless self promotion, but you are of course free to do that if you like.