Add possiblity to send files in request body

[daanvdk]

Adds a possibility to send files deeply nested within data.

To do this you have to send a multipart/form-data request with the data encoded as json in a field called data. The files within this data have to be replaced with null and added to the multipart data as a file, the name of this file should be file:<path> where <path> is the keys that lead to the file joined with ..

Some other notable changes: So because of this I wanted to load json that is a str instead of only bytes, so I removed the .decode() in jsonloads. This is backwards compatible for python >=3.6 since in that release json.loads was changed to also accept binary data.

[stefanmajoor]

The idea is good, and it is getting there. I do miss two things:

• Documentation. Both in the code (describe what new methods do, inline comments) as well as general documentation (this is how the method works). I had to try to figure out what exactly you were trying to implement from the implementation
• Only the good weather scenario is tested for the file upload. Can you also add tests for the edge cases? e.g. what happens if you do not set the "Data", or the "data" is incorrect. O