Add support for complimentary channel output and deadtime.

This patch enables output on the complimentary channels (TIMx_CHyN).
For timers 1 and 8, deadtime can also be inserted when the channels
transition. For the pyboard, TIM8_CH1/CH1N and TIM8_CH2/CH2N can
take advantage of this.
modure: Initial module, using re1.5 (which is based on re1 codebase).

https://github.com/pfalcon/re1.5
modure: Import needed files from re1.5 v0.5.

https://github.com/pfalcon/re1.5
modure: Basic tests.
unix: Add comment about needed dependencies for MICROPY_FORCE_32BIT.
unix: Update comment MICROPY_GCREGS_SETJMP (untested -> undertested).
Merge pull request #900 from dhylands/comp-deadtime

Add support for complimentary channel output and deadtime.
README: Update "unix" section with more info/details.
Merge branch 'modure' of https://github.com/pfalcon/micropython into pfalcon-modure
stmhal: Enable ure module (tests pass on pyboard).
Merge branch 'pfalcon-modure'
Merge pull request #902 from pfalcon/readme-unix

README: Update "unix" section with more info/details.
modure: Upgrade re1.5 to 0.5.1

Changes include:

regexp.h: Add double-include protection.
modure: Make sure that re1.5 compiled in only of modure itself is enabled.

This is achieved by including re1.5 *.c files straight from modure.c .
py: Implement and,or,xor native ops for viper.
py: Implement native load for viper.

Viper can now do: ptr8(buf)[0], which loads a byte from a buffer using
machine instructions.
py: Fix x86 viper code generation, mem8 <-> mem16 for load.
py: Add module weak link support.

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.
stmhal: Enable module weak links.

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.
stmhal: Rename module files to keep consistency with module name.