MT5 Indicator support and more

[Gunther-Schulz]

I have added a few features:

• add support for spreads
• add support for drawing backtrader indicator output to MT5 charts
• add support for accessing MT5 indicator calculations in backtrader and a few smaller changes which I hope you will find useful!

Originally I was planning on doing more testing and error handling, but I don't seem to get around to it these days so if you like have a look at the changes and see if you deem them ready for prime time. In my personal usage, things seem to be working fine.

[Gunther-Schulz]

Hi, I have finally gotten around to updating the README :-O