This matches the coding/layout style of all the other objects.

We don't use alpha/beta/RC, so for us version and release should be the
same, or it leads to confusion (for example, current, 1.9.1 docs are
marked as 1.9 at places).

The idea is to use it for each symbol in builtins.rst.

Cross-reference text/link is implemented as RST substitution, so easy to
consistently.

The idea is to allow to define a kind of "macros" for repeatitive text,
so all occurrances can be updated in one place. Unfortunately, RST doesn't
support replacements with arguments, which limits usefulness of them and
should be taken into account.

As described at
http://www.sphinx-doc.org/en/stable/ext/intersphinx.html#confval-intersphinx_mapping

This will allow to explicitly refer to CPython docs for cross-references.

We have enough terms or references throughout the docs which may be not
immediately clear or have some important nuances. Referencing terms in
gloassary is the best way to deal with that.

Also, update heading of 1st sections to "Functions and types".

The old intro talked about "differences", but there were hardly any
sections describing differences, mostly MicroPython specific features.
On the other hand, we now have real "differences" chapter, though it's
mostly concerned with stdlib differences.

So, try to avoid confusion by changing wording and linking to the other
chapters and contrasting them with what is described in "MicroPython
language".

And in our case, "consistent" is where each word in the heading is *not*
capitalized.

Later versions of jinja2 need it to be in this subdir, and earlier versions
work with it here as well.

It's useful to try different Sphinx versions using virtualenv/venv, so
exclude a common venv dir name from Sphinx processing.

This applies to match.group() and split().

For ARM Thumb2, this increased code size by 12 bytes.

Prior to this patch there were 2 paths for creating the namedtuple, one for
when no keyword args were passed, and one when there were keyword args.
And alloca was used in the keyword-arg path to temporarily create the array
of elements for the namedtuple, which would then be copied to a
heap-allocated object (the namedtuple itself).

This patch simplifies the code by combining the no-keyword and keyword
paths, and removing the need for the alloca by constructing the namedtuple
on the heap before populating it.

Heap usage in unchanged, stack usage is reduced, use of alloca is removed,
and code size is not increased and is actually reduced by between 20-30
bytes for most ports.

The name used in py/mpconfig.h is MICROPY_FLOAT_IMPL so rename this
Makefile variable to mirror that.

By default the firmware is built with single-precision floating point.
To build a particular board using double precision instead, put the
following line in the mpconfigboard.mk file:

    FLOAT_IMPL = double

The while-loop that calls chop_component will guarantee that level==-1 at
the end of the loop.  Hence the code following it is unnecessary.

The check for p==this_name will catch imports that are beyond the
top-level, and also covers the case of new_mod_q==MP_QSTR_ (equivalent to
new_mod_l==0) so that check is removed.

There is also a new check at the start for level>=0 to guard against
__import__ being called with bad level values.

py/builtin.h declares mp_builtin_open with the first argument of type
size_t.  Make all implementations conform to this declaration.

Previously, only "selected chapters" were shown in left-pane ToC (of
Read The Docs theme). These chapters were selected out of order. The
rest of chapters were hidden beyond "Documentation Contents" pseudo-
chapter. This arguably led only to confusion, as many people probably
never tried to open that pseudo-chapter, and those who did, were
confused. Such organization is even worse for PDF output, causing
chapters go in mix-mashed order.

So, instead move to single clean ToC. This will allow readers of HTML
to have access to any doc content at their fingertips (and straight
before their eyes), and will allow to finally have clean PDF docs.