#193: MarshalJSON preserves avro schema ordering

[galion96]

#193

Since avro field order is important, and json.Marshal doesn't preserve the same ordering as struct has, I added this approach (which does generate a fair amount of code) but seems to be working.

I would add the test case for this but not sure since I am not that much into the codebase.
I did however test it locally.

And this way if we have a struct like

fields{ A: "a", C: "c", D: "d", B: "b", Z: "z", E: "e", }
The order would always be after marshaling:

{"a":"a","c":"c","d":"d","b":"b","z":"z","e":"e"}

Edit: now to think about it maybe the template should only call json.Marshal and since it's a struct it should be fine.