[wip] - support for shorting

[ddragosd]

I'm opening a PR to get feedback on adding support for shorting.

I need this feature, and I'd like to share it with the community too.

Details

The implementation intentionally keeps the original behavior in place as much as possible - which is no shorting support . Developers have to be specific in the code to enable it.
What this PR adds:

• MarginWallet - a class that should be explicitly used when shorting is needed. Instead of initializing a Wallet instance, developers can initialize a MarginWallet
• NegativeQuantity - I created this class as the current implementation is pretty strict with throwing errors for negative quantities, and I wanted to leave that functionality untouched.

TODO:

• Add documentation and sample code showing how to setup shorting.

Related Issues

• Feature Request: Support for Shorting #317
• Any plan for short action？ #439
• short trades, down trend and wallet with negative value #327

[spytensor]

Great Job!

[ddragosd]

I'm still testing this in production for a little longer before removing the WIP, and making it ready for review.

[carlogrisetti]

Thanks a lot for your effort!

[BarakBa1]

@ddragosd you should take a look at this implementation from MrDaubinet
could be helpful for your work to support shorting

[ddragosd]

@BarakBa1 thanks for referencing the extension. Are you suggesting we don't merge this PR and instead use the extension you referenced ?

[Buxiulei]

Hope the shorting can be merged into the master

[qwpto]

Thanks for the efforts, hope it gets merged.