Fixed cash settlement of options

[quantx-heiko]

I fixed the cash settlement issue and introduced a helper class with a method for checking if a symbol is cash settled.
Additionally I created unit tests for this method.
This PR relates to #46 .

[quantx-heiko]

@laroche Did you have a look on this already. Is it OK for you?

[laroche]

Great, I've merged your code in, but didn't want to add a new file for this.
I haven't looked at the example lines yet, but hope to find some more time
the next days to look at example input for this.

Thanks a lot,

Florian La Roche

[quantx-heiko]

Thanks, I introduced the helper class because I also implemented Unit Tests for the new method which is checking if the symbol is being cash settled or not.
I'd appreciate to see the unit tests as part of the master code as well. I makes it much more easier for all contributors to see if things break during developing new features or fixing bugs.

[laroche]

Yes, unittests are missing completely right now.
One possibility would be to have a broad set of example trades together with verified/correct tax output
and make sure this set stays correct with all further changes coming in.

best regards,

Florian La Roche

[quantx-heiko]

I absolutely agree, I already started implementing some unit tests with my first contributions to the project.
So I suggest to start with the Helper class and the unit test for cash settlement, I supplied with this pull request.