AP_Scripting: added an example of OOP programming

[tridge]

very useful pattern for more complex scripts

[tridge]

@WickedShell wants to redo this with metatables

[davidbuzz]

I think this should go in till @WickedShell has a chance to do something better. lgtm.

[WickedShell]

Real metatables work nicely, #15653 add's support, and this should be easy to rework on top of that, but I don't have the time before the call to get that done.

[davidbuzz]

As best as i can tell this PR includes a script that does not use 'metatables' but should still work as-is..? Its beyond my knowledge to even know what a metatable is ... or how using them might change this PR, so i'm just trying to move this pr forward..... do we merge it, or close it.? :-)

[tridge]

@WickedShell i've changed the example to include both closure and metatable style of objects
I've tested memory overheads and with closures doing 2 objects costs approx 450 more bytes than using metatables. So for small numbers of objects it really doesn't matter