Document and support `upload` about storj.js HOT 2 CLOSED

This should also be accompanied by uploadData

We need to work on the naming here. get is consistent with the rest of the api (get/create). To keep that symmetry we would have getData and createData. That being said createData seems awkward.

I suggest adding another section to the README.md ## Low Level. The purpose of Low Level is to expose methods that sit between storj-lib and storj.js in their level of "sugar". We can add features to Low Level that may be a bit much for a user new to Storj, Node.js, or JavaScript in general, features that are useful but aren't necessary when just starting. This section is where we can expose primitives and methods designed for performance optimizations.

I'm thinking methods that would be great in this section:

• download (currently getData)
• upload (currently uploadData)
• getFilePointers

And possible future "sugar" for lower level Storj primitives, like contacts, audits, and frames.

from storj.js.

getData and getFilePointers are both implemented. Still need to implement upload.

from storj.js.