Previously to this patch all constant string/bytes objects were
interned by the compiler, and this lead to crashes when the qstr was too
long (noticeable now that qstr length storage defaults to 1 byte).

With this patch, long string/bytes objects are never interned, and are
referenced directly as constant objects within generated code using
load_const_obj.

This allows to directly load a Python object to the Python stack.  See
issue #722 for background.

This enable libc functions, GC, and line-editing function. Also, UART
emulation for POSIX systems is added. Emulation build is set as default.

Unlike bare-arm, which is mostly intended to show raw interpreter size,
without library and support code dependencies. This port is intended to
be a better base to start new ports, and also will include emulation
build to allow debug some aspects of embedded targets on POSIX systems.

This initial commit is verbatim copy of bare-arm code.

Ref issue #699.

This config option is for the USB OTG pin, pin A10.  This is used on
some boards but not others.  Eg PYBv3 uses PA10 for LED(2), so it
shouldn't be used for OTG ID (actually PA10 is multiplexed on this
board, but defaults to LED(2)).

Partially addresses issue #1059.

readline_process_char() can be fed character by character, for example,
received from external event loop. This will allow to integrate MicroPython
into cooperative multitasking systems.

This new config option sets how many fixed-number-of-bytes to use to
store the length of each qstr.  Previously this was hard coded to 2,
but, as per issue #1056, this is considered overkill since no-one
needs identifiers longer than 255 bytes.

With this patch the number of bytes for the length is configurable, and
defaults to 1 byte.  The configuration option filters through to the
makeqstrdata.py script.

Code size savings going from 2 to 1 byte:
- unix x64 down by 592 bytes
- stmhal down by 1148 bytes
- bare-arm down by 284 bytes

Also has RAM savings, and will be slightly more efficient in execution.

Previous patch c38dc3cc allowed any
object to be compared with any other, using pointer comparison for a
fallback.  As such, existing code which checked for this case is no
longer needed.

Return "not equal" for objects that don't implement equality check.
This is as per Python specs.

Compiler optimises lookup of module.CONST when enabled (an existing
feature).  Disabled by default; enabled for unix, windows, stmhal.
Costs about 100 bytes ROM on stmhal.

Similar to ffi_float.py.

This allows to enable mem-info functions in micropython module, even if
MICROPY_MEM_STATS is not enabled.  In this case, you get mem_info and
qstr_info but not mem_{total,current,peak}.

Replaces RUN_TEST=1 definition; now "make test" in qemu-arm directory
will run tests/basics/ and check that they all succeed.

This patch also enables the test on Travis CI.