2 new functions and 1 modified and slight add-ons

[mdjames094]

Hello,

For my own usage, i needed to complete the set of tools with functions allowing to cancel open trades [cancel_open_trades()] or close open positions [close_open_positions()]. These functions accept a list of symbols as parameter or can operate on all trades/positions if no parameter is specified.

I also modified the get_current_securities and made slight addon/adjustments to other functions.

I am quite new to python but have a good knowledge of R. Please forgive my bad english.

Best regards, mdjames.