Fix #18007 : Document CookieJar.add_cookie_header request parameter changes in 3.3 and 3.4.

Patch by Guilherme Simões.

an internal XML encoding is UTF-8 or US-ASCII.

an internal XML encoding is UTF-8 or US-ASCII.

size and pickling time.

namespace as string.

when applicable.

on OS-X. Patch by Jeff Ramnani.

This has come up often enough now on the tracker that it deserves a FAQ entry.

* Describe compress() and accumulate()
* Add a subsection on combinatoric functions.
* Add a forward link to skip the theoretical discussion in the first section.
* Clarify what filterfalse() is the opposite of.
* Remove the old outline and some notes at the end.
* Various small edits.

initial patch by Trent Nelson.