Add JSON output option to fitdump script

[pR0Ps]

Other minor things:

• Removed non-implemented output formats
• Removed the restrction on dumping non-readable formats to stdout
• Allow Python to buffer the output for faster execution

Fixes #41

[gamb]

Works great 👍. And fwiw, I'm actively using this patch for a project.

[gamb]

One query... Is "type" always = "data"? Assume != "data" would be anomalous, err… "data".

[gamb]

For my use case at least, this format made more sense:

         if isinstance(obj, fitparse.DataMessage):
             return {
-                "name": obj.name,
-                "type": obj.type,
-                "data": {
-                    data.name: data.value for data in obj
-                }
+                "type": obj.name,
+                "properties": { data.name: data.value for data in obj }

Sample:

{
        "properties": {
            "event": "session",
            "event_type": "stop",
            "first_lap_index": 1,
            "message_index": 1,
            "num_laps": 7,
            "sport": "running",
            "start_time": "2016-05-03T17:28:13",
            "timestamp": "2016-05-03T18:12:48",
            "total_elapsed_time": 2420.949,
            "total_timer_time": 2420.949
        },
        "type": "session"
    },
    {
        "properties": {
            "event": "activity",
            "event_type": "stop",
            "local_timestamp": "2016-05-03T19:12:48",
            "num_sessions": 2,
            "timestamp": "2016-05-03T18:12:48",
            "total_timer_time": 2676.859,
            "type": "manual"
        },
        "type": "activity"
    }

[pR0Ps]

@gamb The type of a DataMessage will always be "data" so yep, when dumping to JSON the type will always be "data". Good catch, I've applied your change.

[dtcooper]

Looks like a very sane approach to me, @pR0Ps. Thanks for adding this!