Formalize datetime output format

[newsch]

Currently ABE outputs datetimes in this format: "Sun, 06 Aug 2017 09:00:00 GMT".

It would be better to use a standard like ISO8601: "2017-08-06T09:00:00". Futureboard was having trouble parsing that specific string with their date library, and it makes sense to have control over the output of the API.

This could be done by extending Flask's JSONEncoder like so:

from flask.json import JSONEncoder

class CustomJSONEncoder(JSONEncoder):

    def default(self, obj):
        if isinstance(obj, datetime):
            return obj.isoformat()
        else:
            return JSONEncoder.default(self, obj)


app = Flask(__name__)
app.json_encoder = CustomJSONEncoder