Fixes FUD around ASI

ASI was being referred to as something that changes the behaviour of someone's code at will, like a non-deterministic parser, which couldn't be further from the truth. This patch fixes that by explaining how the ASI rules work instead.

More information on ASI can be found in this site:

http://aresemicolonsnecessaryinjavascript.com/

In particular, Inimino's post is terrific on explaining everything about it, while still managing to be pretty neutral on a particular style — as that's the only thing that should drive the use or not of ASI.