Updated teensy to build.

Refactored some stmhal files which are shared with teensy.
Added hexfile target
Add copysignf

* Fix #692
Add timer_deinit and call it just before doing a soft-restart

This fixes #733.
modffi: Add special 'C' code for passing a callback function pointer.
stackctrl: Add "mp_" prefix.
Try not to cause a MemoryError when raising an exception during nterrupt handling.

Step 1 fixes #732
Merge pull request #734 from iabdalkader/copysign

Add copysignf
Merge branch 'preserve-except' of github.com:dhylands/micropython into dhylands-preserve-except
py, objexcept: Only check for locked gc if gc is enabled.
Merge branch 'dhylands-preserve-except'
Merge branch 'teensy-new' of github.com:dhylands/micropython into dhylands-teensy-new

Conflicts:
	stmhal/pin_named_pins.c
	stmhal/readline.c

Renamed HAL_H to MICROPY_HAL_H.  Made stmhal/mphal.h which intends to
define the generic Micro Python HAL, which in stmhal sits above the ST
HAL.
Merge branch 'dhylands-teensy-new'
Merge pull request #709 from windelbouwman/master

Added hexfile target
Merge branch 'add-timer-deinit' of github.com:dhylands/micropython into dhylands-add-timer-deinit
stmhal: Some reordering of code/functions.
Merge branch 'dhylands-add-timer-deinit'
qemu: fix typo in readme
Merge pull request #739 from errordeveloper/patch-1

qemu: fix typo in readme
Rename machine_(u)int_t to mp_(u)int_t.

See discussion in issue #50.