Small hash tables (eg those used in user class instances that only have a
few members) now only use the minimum amount of memory necessary to hold
the key/value pairs.  This can reduce performance for instances that have
many members (because then there are many reallocations/rehashings of the
table), but helps to conserve memory.

See issue #1760.

Don't describe just single port's peculiarities, note aboute possible
array of issues with floating-point.

Should fix issue #1947.

"" is the correct name of the root directory when mounting a device there
(as opposed to "/").  One can now do os.listdir('/') and open('/abc'), as
well as os.listdir() and open('abc').

These are *defined* per-port, but why redeclare them again and again.

A shortcut for users to provide background diagnostic info for bug
reports.

The qstr data needs to be turned into a proper C string so non-ASCII
chars must be properly escaped according to C rules.

Most grammar rules can optimise to the identity if they only have a single
argument, saving a lot of RAM building the parse tree.  Previous to this
patch, whether a given grammar rule could be optimised was defined (mostly
implicitly) by a complicated set of logic rules.  With this patch the
definition is always specified explicitly by using "and_ident" in the rule
definition in the grammar.  This simplifies the logic of the parser,
making it a bit smaller and faster.  RAM usage in unaffected.

esponewire.c contains low-level timing-critical functions that go in
iRAM.  modonewire.c contains Python wrapper code.

Now pins can be easily looked up in the table using the pin number as the
index and vice versa.

This field is the same as phys_port and not needed.

Non-printable characters are escaped as 0xXX, where XX are the hex
digits of the character value.

frozentest.py is frozen into the binary as frozen bytecode.  The .mpy
file is included so that there is no dependency on the cross compiler.

The config variable MICROPY_MODULE_FROZEN is now made of two separate
parts: MICROPY_MODULE_FROZEN_STR and MICROPY_MODULE_FROZEN_MPY.  This
allows to have none, either or both of frozen strings and frozen mpy
files (aka frozen bytecode).

Currently it can freeze .mpy files.

It's needed by frozen bytecode.

It costs 1188 bytes of code on Thumb 2 archs.