Network support in stmhal, and improved viper compiler.

Changes in core:
- tidy up native emitter and assemblers
- viper can compiler more binary ops
- viper supports casting (int, ptr8, ptr16)
- viper can compile native stores (eg p[1] = 42)
- remove IOError (use OSError instead)

stmhal port:
- fix OSX mass storage issue, so pyboard can be left plugged in
- add network and usocket modules with CC3000 and WIZnet5k support
  (disabled by default)
- improved percent option in timer PWM
- add pyb.elapsed_millis, pyb.elapsed_micros
- internal flash is labelled as "pybflash" on creation
- don't init NSS pin when initialising SPI bus with NSS_SOFT mode

Changes in core:

- bytecode prelude uses less RAM
- free non-interned strings earlier
- add builtins module
- add ujson module with dumps and loads
- mpz div changed so that mpz is more efficient
- some compiler optimisations
- some simplifications of the code
- bug fix memcpy -> memmove
- changed most instances of int/uint to mp_int_t/mp_uint_t
- added ioctl method to stream protocol
- divmod, % and // support for floating-point numbers

Native emitter enhancements:
- bug fixes
- support for delete name and global
- support for end finally
- x86 support
- x86-64 can use extended regs

unix port:
- MIPS compilation support

stmhal port:
- add generic select module
- ability to select/poll on UART objects
- proper SDHC support (cards > 4gb now work)
- enhanced timer support (PWM, OC, IC)
- big fix with miss-aligned stack pointer
- more math functions implemented

Added drivers subdirectory with WIZNet5200 support
(disabled by default).

Added docs subdirectory and moved to Sphinx docs.

Improved teensy support.

Bug fixes, viper improvements, and more

New features in core:
- min and max accept key= argument
- accepts user defined ==, >, <=, >=
- native support for ARM (non thumb)
- cut RAM and ROM usage of zlibd
- significant GC allocation speed up

Viper improvements:
- type annotations
- store to global
- call functions with native types
- raise exceptions

Bug fixes to core:
- fix multiplication of a sequence by negative number
- GC bug fix where native code was being collected
- int(b'1234') now works
- can now make strings longer than 64k

unix port:
- modtermios for unix
- make install for unix

stmhal port:
- reduced code size by 35k
- put some code into first 16k block
- in safe mode SD card is still presented as MSD
- SD card init fixes; should be more reliable
- added time.mktime; enhanced time.localtime
- new Pin functions: mode, pull, af
- nestable enable_irq/disable_irq
- added pyb.micros()
- added USB_VCP.any()
- STM32F4DISC accel support via staccel.py script

v1.3: New features and many bug fixes.

New features include:
- file.flush, os.stat
- unicode enabled by default on unix and stmhal ports
- print function accepts file= argument
- I2C object allows for 16-bit mem addr
- emergency exception buffer for improved exception traceback
- USB_VCP object
- 0:/ and 1:/ changed to /flash and /sd
- improved Pin object
- can set pin alternate function from Python
- builtin reversed, can len() and subscr range objects
- added moductypes
- added modzlibd for DEFLATE decompression

Code improvements include:
- more efficient line-number to bytecode mapping
- new STM HAL driver v1.3.0

Bug fixes include:
- mpz (bignum) fixes
- accel startup improved
- important bug fix in GC

v1.2: Unicode support (disabled by default); bug fixes and minor feat…

…ures added.

v1.1.1: Improved LCD driver, UART REPL and some bug fixes.

Bumping version because this binary will be put on the next batch of pyboards.

v1.1: Many bug fixes, enhancements and features.

v1.0.1: mostly bug fixes for stmhal/, features for py/.

Main bug fixes: flushing USB CDC correctly, setting RTC.

Main features for stmhal: improved native and viper emitters.

This version goes on the next batch of pyboards.

Version 1.0! This is shipping with the next batch of pyboards.

Preparing for v1.0.