Parse track files to json

[Luc-Veldhuis]

The handy provided parser has a json option which uses the Rust pretty print output.
Eventhough this is already great for viewing the track files, it makes parsing in other tools a little harder.
In #100 I tried to add serialization from the serde_derive library to output valid json.

[spinpx]

Thanks @Luc-Veldhuis