Added Partial Serialization support + Missing Default & Debug derives

[AnneKitsune]

Allows using serde to serialize rigidbodies among other things.

[L-as]

I updated this to work with the latest version of nphysics: https://github.com/Laaas/nphysics

[sebcrozet]

@laaas Thank you for updating this! Would you mind porting your changes in this PR, or perhaps open a new one?

Also, could you please double-check that the serde-serialize feature of nalgebra is really not enabled if ncollide's serde feature isn't enabled either. If I remember correctly there is some kind of Cargo bug that unifies all the features independently from the target.cfg statements. One way of checking this is to compile (in verbose mode) ncollide without the serde feature and see if the command line compiling nalgebra includes the serde-serialize feature or not.

[L-as]

You are unfortunately right.

[sebcrozet]

@laaas Thank you for checking. I guess one way of working around this is to add a feature serde-serialize = [ "serde", "nalgebra/serde-serialize" ] to ncollide instead of all those target.cfg.

[L-as]

@sebcrozet what should I do with this PR then?

[AnneKitsune]

You can make a pull request over my fork and it will update this pull request.