Made with-shutdown! take variable # of pools

Made with-shutdown! take a variable number of pools. Also changed README
to make with-shutdown! more prominent.
Clarify why John Claypoole links to Betsy Ross.
Add priority threadpools.
README cleanups.
Fix description of which priority is used
Made priority-fn act on *seq* of arguments
Additional docs on threadpools

Also fixed my "fix" of innermost/outermost priority.
Fix lazy read bug.

Input sequences were not actually read lazily! I added a test and caught
it, so I fixed it also.
Minor cleanups and comments.
Merge branch 'master' into pre-release

Conflicts:
	project.clj
	test/com/climate/claypoole_test.clj
Updated changelog.
Made README pmap description positive
Test and fix bug for upmap scheduling exceptions
Test chaining of pmaps.
Expose thread-factory.
Use ScheduledExecutorService
Addressed Sebastian's first comments.
Resolved most of Sebastian's comments
priority-fn is applied to list of args
Fix lint warning