This changes the main documentation, doc strings, source code comments, and a
couple error messages in the test suite. In some cases the word was removed
or edited some other way to fix the grammar.

Patch from Matheus Vieira Portela.

Initial patch by Kinga Farkas, Martin Panter, and John Posner.

Patch by Martin Panter.

Original patch by Martin Panter.

and set comparisions.  Patch by Gareth Rees.

Also updates a few internal implementations of the same thing to use the
new built-in code.

Contributed by Arnon Yaari.

Patch by Martin Panter.

Reported by Jon Colburn on docs@.

- clarified the distinction between text encodings and other codecs
- clarified relationship with builtin open and the io module
- consolidated documentation of error handlers into one section
- clarified type constraints of some behaviours
- added tests for some of the new statements in the docs

Add an entry in the language datamodel special methods section.
Revise and index its discussion in the stdtypes mapping/dict section.

Patch by Alexander Belopolsky.

Patch by Raúl Cumplido.

Also, attempt to reduce confusion in the glossary by not saying there are
different "types" of arguments and parameters.