Add arbitrary precision integer support.

Some functionality is still missing (eg and, or, bit shift), and some
things are buggy (eg subtract).
Merge branch 'master' of github.com:micropython/micropython
Add Configurable LFN support to FatFS
Merge pull request #316 from iabdalkader/fatfs_lfn

Add Configurable LFN support to FatFS
stm: Add USART enum for pyboard skin labels.
stm: Make pendsv_nlr_jump work when debugging is enabled.

Stack layout is different when -g used, so need to handle the pendsv
jump differently.  Addresses Issue #315.
Add EXTI support

Revamp usrsw to use new exti code.
Add user switch callback function.
stm: Add option to pyb_usb_dev_init() to use USB HID interface.

With this option selected, only HID on its own works, not VCP+HID.
py: Fix mpn_sub, was increasing wrong source pointer.

Also change int -> machine_int_t where appropriate.
Fix floating point printing of negative numbers in the range (0, -1.0)
Print an error if a non-valid BOARD is specified.
Update LED configuration
Merge pull request #323 from dhylands/fix-float-print

Fix floating point printing of negative numbers in the range (0, -1.0)
Merge pull request #318 from dhylands/exti

Add EXTI support
Merge pull request #324 from dhylands/board-check

Print an error if an invalid BOARD is specified
Merge pull request #325 from dhylands/led

Update LED configuration
stm: Open header file in text mode (in make-pins).
py: Start to implement shl/shr for mpz.  Fix return void.
py: Remove name of var arg from macros with var args.
stm: Reinstate code to handle CC3000 EXTI (commented out for now).