Add Attributes to URI

[cupOJoseph]

this is what the URI should look like:

{
  "description": "....", 
  "external_url": "...", //havent set one of these yet
  "image": "base64 stuff here", 
  "name": "...",
  "attributes": 
[
    {"trait_type": "Collateral Token", "value": 0xabc123},
    {"trait_type": "Collateral Amount", "value": 5000000000000000},
    ...
 ]
}

json is now valid and contains useful info. Example output:
https://gist.github.com/cupOJoseph/ac67c2af41e77f2e829f9a5bd0aa9140

We should have some direct tests of the output too possibly, so I added a to-do. in the test file.

[cupOJoseph]

looks like failing tests might be unrelated? I think this is ready for review