Also, usocket.readinto(). Known issue is that .readinto() should be available
only for binary files, but micropython uses single method table for both
binary and text files.

Addresses issue #915.

Addresses issue #912.

Just like they handled in other read*(). Note that behavior of readline()
in case there's no data when it's called is underspecified in Python lib
spec, implemented to behave as read() - return None.

This is CPython-compatible convention established yet in acb13886.

The code previously assumed that only functions can be closed over.

Previously, a realloc to a smaller memory chunk size would not free the
unused blocks in the tail of the chunk.

Remove zlibd, superceded by uzlib

Module "uzlib" - based on similarly named library

https://github.com/pfalcon/uzlib

os, time, select modules are now prefixed with u, but are still
available (via weak links) as their original names.

ure and ujson now available as re and json via weak links.

With this patch a port can enable module weak link support and provide
a dict of qstr->module mapping.  This mapping is looked up only if an
import fails to find the requested module in the filesystem.

This allows to have the builtin module named, eg, usocket, and provide
a weak link of "socket" to the same module, but this weak link can be
overridden if a file by the name "socket.py" is found in the import
path.

Viper can now do: ptr8(buf)[0], which loads a byte from a buffer using
machine instructions.

This is achieved by including re1.5 *.c files straight from modure.c .

Changes include:

regexp.h: Add double-include protection.

README: Update "unix" section with more info/details.