able to increase position

[hjchan]

#15
@askibin Created a draft PR based on this issue. I am thinking of combining add collateral and increase position in 1 endpoint because the user might need to add collateral when the user increases position. Although it can be done in bundling the instructions, it will always require adding collateral to be the first instruction to prevent check_leverage failure.

Let me know any comments about this approach, will update decrease position if everything is alright. Thanks

[mabrehan]

Whenever a position is being updated, we are charging borrow_fee. Instead can we update that in unrealized_loss and charge it at the time of closing the position.

[hjchan]

Whenever a position is being updated, we are charging borrow_fee. Instead can we update that in unrealized_loss and charge it at the time of closing the position.

good idea, updated