Update XMLParser.close documentation and fix formatting.

Using ``method`` markup because the method is on a callback object, not an
explicitly documented method. :meth: markup creates links within the current
class which is incorrect.

In addition, indent the paragraph correctly.
#18803: fix more typos.  Patch by F?vry Thibault.
Clarify pyexpat documentation in StartElementHandler
#18839: document that sys.exit() will not accept a non-integer numeric value as exit status.