RFR(s): 8132800: clarify stream package documentation regarding sequential vs parallel modes

[Stuart Marks]

Hi all,

The sequential() and parallel() methods on a stream set the execution mode for 
the entire pipeline. Unfortunately this isn't particularly clear from the 
documentation. This has been a recurring question. Please review this change to 
the java.util.stream package documentation to help clarify this point.

I've also added a couple anchor tags that were missing from various sections.

This is intended to be a purely editorial change, not a specification change.

Bug:

	https://bugs.openjdk.java.net/browse/JDK-8132800

Webrev:

	http://cr.openjdk.java.net/~smarks/reviews/8132800/webrev.0/

Thanks,

s'marks