It defines types used by all other headers.

Fixes #691.

In generalize case, optimization options should be passed to all stages of
the build process.

Expected to be set on command line, with the idea being that for different
targets, there're different smartass ABIs which strive to put unneeded
sections into executables, etc., so let people have flexible way to
strip that.

The option name is similar to previously introduced CLFAGS_EXTRA &
LDFLAGS_EXTRA.

One thing is wanting to do 1 / 2 and get something else but 0, and quite
another - doing rocket science ;-).

Add more DEBUG_printf statements to trace gc behaviour

char can be signedness, and using signedness types is dangerous - it can
lead to negative offsets when doing table lookups. We apparently should just
ban char usage.

In preparation for unicode support.

We still have that char vs byte dichotomy, but majority of string operations
now use byte.

This will allow roughly the same behavior as Python3 for non-ASCII strings,
for example, print("<phrase in non-Latin script>".split()) will print list
of words, not weird hex dump (like Python2 behaves). (Of course, that it
will print list of words, if there're "words" in that phrase at all, separated
by ASCII-compatible whitespace; that surely won't apply to every human
language in existence).

Getting a length of string may be expensive, depending on the underlying
implementation.

void* is of unknown size

Functionality we provide in builtin io module is fairly minimal. Some
code, including CPython stdlib, depends on more functionality. So, there's
a choice to either implement it in C, or move it _io, and let implement other
functionality in Python. 2nd choice is pursued. This setup matches CPython
too (_io is builtin, io is Python-level).

It needs to be reused for generator functions, too.

At this point, start will be >= 0, so checking if stop < 0 is redundant with
checking if start > stop a few lines later.

This is getting more and more tangled, but that's old news.

As before, instead of pushing constant values on stack again and again, just
pass around pointer to a structure.

Should finish addressing issue #524.

Ports which wants to have it, should define MICROPY_PY_SYS_PLATFORM to a
string value they need.

Benefits: won't crash baremetal targets, will provide Python source location
when not implemented feature used (it will no longer provide C source
location, but just grep for error message).

This reduces stack usage by 16 words (64 bytes) for stmhal/ port.

See issue #640.

?= operator does not do delayed expansion (unlike =).

- Move the includes for alloca() intp mpconfigport.h

  there are special tweaks and paths to be considered. Just provide some
  defaults, in case the values are undefined.
- py-version.sh does not need any bash specific features.
- Use libdl only on Linux for now. FreeBSD provides dl*() calls from libc.