fix bug in the DemoData()

The demo data is now usable. Now it simulates a real payload coming from a http request instead of raw abstract text. Another fix was the resulting output from DemoData: now it returns a Buffer, in order to provide the same thing that you should receive in a real environment.

This version was tested using a very sensitive file upload: a zip and rar files, which are later verified for data consistency when you try uncompress them. Everything was successfull.

(Thanks for reporting, Thomas Edwards :)

a small fix in the readme

a bad name was in the readme.md file: the "require" call should be: "parse-multipart" instead of "multipart"