Edit APIException to accept string for additional field

[rserna2010]

Fix #41

[mjallday]

can you also assert the extras?

here's an example of how to generate non-blank extras

curl https://api.balancedpayments.com/cards/CC5uc1B6fJPQBSJUi0m58tal/credits \
    -u ak-test-1o9QKwUCrwstHWO5sGxICtIJdQXFTjnrV: \
    -d "amount=0"

which gives you

{
  "errors": [
    {
      "status": "Bad Request",
      "category_code": "request",
      "additional": null,
      "status_code": 400,
      "category_type": "request",
      "extras": {
        "amount": "\"0\" must be >= 1"
      },
      "request_id": "OHMa7081610435611e4ac8902b12035401b",
      "description": "Invalid field [amount] - \"0\" must be >= 1 Your request id is OHMa7081610435611e4ac8902b12035401b."
    }
  ]
}

[mjallday]

@rserna2010 this is a breaking change. it requires you to bump the version number appropriately so that customers do not upgrade to this version and break their code.

lgtm.

[remear]

@rserna2010 I believe right now bumping versions requires changing it in the following locations:

https://github.com/balanced/balanced-csharp/blob/master/Balanced/Properties/AssemblyInfo.cs#L35-L36
https://github.com/balanced/balanced-csharp/blob/master/Balanced/Balanced.cs#L13

In the near future we should change https://github.com/balanced/balanced-csharp/blob/master/Balanced/Balanced.cs#L13 to read the version from the assembly so version bumping is easier. #44

Go ahead and merge this when you're ready, then bump the versions in master. I can deploy it to nuget later tomorrow. I recall the process being somewhat complicated still and not yet in the README. Just ping me when it's ready to go out.