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.