Made @bindable decorator do a bit of sanity checking on what it's decorating
Tightened up UserConfig __dir__ and __iter__...

to account for the possibility of using existing attribute names as dict keys,
which is not allowed!
Added configuration of GST_LOG* environment variables...

so that we can tell gstreamer to log messages to a file!
Moved clamp to util file, fixed issue when bound is zero
Added seeking behaviour...

It's a bit choppy at the moment, just like volume changes - will investigate
using a controller to smooth out things at some stage.
Updated .gitignore