Add an option for KeepNewLinesInDescription flag

[eddieowens]

As part of #109, all newlines from descriptions were removed but in some cases I want to preserve them e.g. when using the description field for display in a gitbook site. Would it be possible to add an option for the KeepNewLinesInDescription flag in here?

I'd be completely willing to make the PR as well.

[tzahush]

@chrusty , looks like we got another demand here!
this is solved by #179