In odoo/documentation-user#945, the developer documentation is merged
with the user documentation in a single repository and build config.

This commit then removes source files for the developer documentation
from the odoo/odoo repository.

DOC PR: https://github.com/odoo/documentation-user/pull/945

task-2351938
task-2352371
task-2205684
task-2352544

Co-authored-by: Victor Feyens <vfe@odoo.com>
Co-authored-by: Antoine Vandevenne <anv@odoo.com>

Odoo no longer supports python 2, thus some of these helpers can and
have been replaced by python 3 built-ins, therefore there is no need for
them to stay defined.

The removed helpers are:
    * izip, imap and ifilter
    * unichr, text_type
    * implements_to_string, implements_iterator
    * string_types, integer_types
    * to_native

The python 2 shims have also been removed, and only the python 3 helpers
have been kept, because they can still be usable (i.e. accepting
both bytes and str for functions that can only accept one of the two)

[REM] pyjsparser: remove PY3 shims

They're no longer necessary as Odoo doesn't officially support python 2
anymore.

closes odoo/odoo#28519

This commit replaces calls to pycompat helpers that were intended for
python 2 <-> python 3 interoperability for python 3 builtins, as python
2 is no longer officially supported by Odoo.

This includes:
    * calls to imap/izip/ifilter replaced by map/zip/filter
    * uses of text_type replaced by str
    * uses of unichr replaced by chr
    * calls to implements_to_string, implements_iterator removed
    * string_types and integer_types replaced by str, int respectively
    * calls to to_native replaced by calls to to_text

This is done in preparation to the removal of these deprecated helpers
in the following commit.

Now that we're closer to switching to P3 for good, these helpers have
outlived their usefulness, and mostly add noise.

All remaining dict.iter*() or dict.view*() must be converted to the
normal keys(), values() or items() calls.

Whenever the result is likely to be used for more than the scope of a
loop, or when the dict needs to be modified during iteration, the calls
must be wrapped in a ``list()``, to protect the new P3 semantics.
Those cases are very exceptional.

Also removed some dead code or improved the API to remove unnecessary
conversions.

* StringIO removed from stdlib, replace with io
* try to correctly handle BytesIO/StringIO (one is for bytes the other
  is for text)
* fix base64: Python 3 removed bytes-encoding and bytes-bytes
  codecs (via #encode) so replace all calls to str.encode('base64'),
  also b64encode is a bytes->bytes conversion so attempt to properly
  handle that

issue #8530

* add Sphinx 1.6 compatibility (use app.set_translator when
  available as in that case programmatically setting
  html_translator_class is broken)
* fix a bunch of code block lexers to avoid warnings & get better
  coloration
* add a few options which were referred to without being actually
  defined
* fix some rST formatting