modffi: Describe typecodes where they differ from used by struct module.

Exact behavior of typecodes may be not yet enforced.
modffi: Don't use OSError for clearly unrelated errors.
objexcept: Add mp_obj_new_exception_arg1() convenience function.
unix: OSError's args[0] should be errno numeric value.

Well, Python3 also defines an attribute for that, but that's bloat.
modsocket: Clean up OSError-like exception a bit.

Some BSD socket functions don't return error numbers in errno namespace, but
rather in other error namespaces. CPython resolves this by using OSError
subclasses for them. We don't do that so far, so there's ambiguity here.
unix: Workaround MP_OBJ_NEW_SMALL_INT() 64-bit issues.
builtinimport: If there was error compiling imported module, raise exception.
emitglue: Typo fix in var name.
showbc: MAKE_CLOSURE*: Update for new closed-over encoding.
vm: Add rudimentary bytecode execution tracing capability.
objexcept: Don't store args tuple within exception object.

To avoid pointer-to-field GC problem.
windows/README: Use CROSS_COMPILE instead of CC to cover other tools too.

Suggested by @lurch.
Makefile: Allow to override "super optimization" options used for some files.

To help with debugging issue like #510 for example.
Merge pull request #518 from pfalcon/vm-trace

vm: Add rudimentary bytecode execution tracing capability.
Merge pull request #519 from pfalcon/exc-no-ptr-to-field

objexcept: Don't store args tuple within exception object.
py, vm: Free heap-allocated state if it was allocated on the heap.
py, vm: Fix recent bug where state is freed too early.
Merge pull request #515 from errordeveloper/qemu

Qemu
py, gc: Fix old gc_realloc for case when NULL is passed in as ptr.
py: Support instance __call__ method.