Reduces code size.

This refactoring saves code space.

Code size change in bytes for this patch is:

   bare-arm:   -72
minimal x86:   -48
   unix x64:   -32
unix nanbox:  -120
     stmhal:   -68
     cc3200:   -64
    esp8266:   -56

This dev board only has a single USB connector, connected to the FS
peripheral.

The line in docs/conf.py with the release/version number was recently
changed and this patch makes the makeversionhdr.py script work again.

Previous to this patch hexlify(b'', b':') would lead to a bad crash due to
the computed length of the result being -1=0xffffffff.

The simple NTP client module is named "ntptime.py".

This makes top-level ToC of the pyboard docs consistent with other ports
(consisting of 3 chapters: QuickRef, General Info, and Tutorial).

Also, some other minor tweaks applied, like local ToC for General Info and
headings mentioning pyboard.

This pseudo-section causes artifacts with latexpdf generation (almost
empty page with list containing literal "genindex", "modeindex", "search"
items). For HTML docs, these sections can be accessed from "home" page.

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.