Changed iOS to use NSParagraphStyle instead of CTParagraphStyle

I was getting a crash when trying to run `boundingRectWithSize:options:context:` on an attributed string that was parsed and required a paragraph style. I do not believe NSParagraphStyle is bridged with CTParagraphStyle on iOS, thus the crash. I just added a conditional compilation statement to use NSParagraphStyle on iOS and the original code for everything else.