Instead of compiler-level if-logic.  This is necessary to know what error
strings are included in the build at the preprocessor stage, so that string
compression can be implemented.

So this setting could be used by other source files if needed.

This commit makes all functions and function wrappers in modubinascii.c
STATIC and conditional on the MICROPY_PY_UBINASCII setting, which will
exclude the file from qstr/ compressed-string searching when ubinascii is
not enabled.  The now-unused modubinascii.h header file is also removed.

The cc3200 port is updated accordingly to use this module in its entirety
instead of providing its own top-level definition of ubinascii.

This was originally like this because the cc3200 port has its own ubinascii
module which referenced these methods.  The plan appeared to be that the
API might diverge (e.g. hardware crc), but this should be done similar to
I2C/SPI via a port-specific handler, rather than the port having its own
definition of the module.  Having a centralised module definition also
enforces consistency of the API among ports.

The idea here is that there's a moderate amount of ROM used up by exception
text.  Obviously we try to keep the messages short, and the code can enable
terse errors, but it still adds up.  Listed below is the total string data
size for various ports:

    bare-arm 2860
    minimal 2876
    stm32 8926  (PYBV11)
    cc3200 3751
    esp32 5721

This commit implements compression of these strings.  It takes advantage of
the fact that these strings are all 7-bit ascii and extracts the top 128
frequently used words from the messages and stores them packed (dropping
their null-terminator), then uses (0x80 | index) inside strings to refer to
these common words.  Spaces are automatically added around words, saving
more bytes.  This happens transparently in the build process, mirroring the
steps that are used to generate the QSTR data.  The MP_COMPRESSED_ROM_TEXT
macro wraps any literal string that should compressed, and it's
automatically decompressed in mp_decompress_rom_string.

There are many schemes that could be used for the compression, and some are
included in py/makecompresseddata.py for reference (space, Huffman, ngram,
common word).  Results showed that the common-word compression gets better
results.  This is before counting the increased cost of the Huffman
decoder.  This might be slightly counter-intuitive, but this data is
extremely repetitive at a word-level, and the byte-level entropy coder
can't quite exploit that as efficiently.  Ideally one would combine both
approaches, but for now the common-word approach is the one that is used.

For additional comparison, the size of the raw data compressed with gzip
and zlib is calculated, as a sort of proxy for a lower entropy bound.  With
this scheme we come within 15% on stm32, and 30% on bare-arm (i.e. we use
x% more bytes than the data compressed with gzip -- not counting the code
overhead of a decoder, and how this would be hypothetically implemented).

The feature is disabled by default and can be enabled by setting
MICROPY_ROM_TEXT_COMPRESSION at the Makefile-level.

The decompression of error-strings is only done if the string is accessed
via printing or via er.args.  Tests are added for this feature to ensure
the decompression works.

Enabled on: bare-arm, minimal, unix coverage/dev/minimal, stm32, esp32,
esp8266, cc3200, teensy, qemu-arm, nrf.  Not enabled on others to be able
to test the code when the feature is disabled (the default case).

Code size change for this commit:

   bare-arm:  -600 -0.906%
minimal x86:  -308 -0.208%
   unix x64:    +0 +0.000%
unix nanbox:    +0 +0.000%
      stm32: -3368 -0.869% PYBV10
     cc3200: -1024 -0.558%
    esp8266: -2512 -0.368% GENERIC
      esp32: -2876 -0.205% GENERIC[incl -3168(data)]
        nrf: -1708 -1.173% pca10040
       samd:    +0 +0.000% ADAFRUIT_ITSYBITSY_M4_EXPRESS