User options

[rpapallas]

Hello,

I needed some way to get some "user options". I have different MuJoCo data that I would like to visualize, so I wanted a way for a user to press "1" and then the client code alter the viewer data/model to the first data, then press "2" and alter the viewer data/model to the second data etc.

I have written this here: rpapallas@dc8679e

If you think something like this is going to be useful and could be implemented like this or differently, please let me know. This could be a generic feature like "user options" allowing the client code to do something if a certain user option is pressed, which currently is limited to numeric values, but could be any value while shift is pressed. I understand that this might not be useful to everyone, though.