Add Content-Type header to HTTP responses for JSON data.

[benmkent]

Adds explicit JSON type to HTTP responses to address #23 .

To achieve this, successful responses must be explicitly given the HTTP status code 200.

[benmkent]

@thealanjason I created a new branch as in my fork the other pieces are a bit tangled up. This is should update all the HTTP responses to explicitly specify the content type is JSON, and MATLAB will understand the responses.

[thealanjason]

Hi @benmkent

thanks for creating a new PR!

Could you please:

1. add the Content-Type to all the HTTP requests as well. For example: update https://github.com/benmkent/UMBridge.jl/blob/5215be52db6b424b5cc191a4459cd15f4c43e770/src/UMBridge.jl#L37 to response = HTTP.request("POST", url(model) * "/Evaluate", ["Content-Type"=>"application/json"], body=JSON.json(body))
2. bump the version number to "1.1.8" in the Project.toml

I've added a separate issue to add tests to check for the "Content-Type" in the header, which can be worked upon later when this is uniformly implemented for all languages that UMBridge supports.

[benmkent]

I have messed up the branch and I have not got time to fix this at the moment due to starting a new position on Monday, I will address this in the future.

It might be possible to fix the JSON issues directly from the MATLAB side, in line 19-24 of the HTTPModel class. I believe this is where MATLAB gets confused about the content type using the "send" function.