Turn off full tests in string-format.py

Add some basic coverage tests
Fix pyb.Led(n) code to work properly.
Fix INT_BUF_SIZE to work with 32-bit and 64-bit
Reduce stack usage of pfenv_print_strn
Merge pull request #408 from dhylands/str-quick-tests

Turn off full tests in string-format.py
Merge pull request #411 from dhylands/pfenv-64-bit

Fix INT_BUF_SIZE to work with 32-bit and 64-bit
Merge pull request #410 from dhylands/fix-led

Fix pyb.Led(n) code to work properly.
Merge pull request #412 from dhylands/pfenv-strn-stack

Pfenv strn stack
py: Make pfenv.c conform to code conventions.
py: Fix math.{ceil,floor,trunc} to return int.
py: Add support for sep and end keywords in print.
tools: Add pip-micropython to install packages in MicroPython-friendly way.
py: Allow multiple of str/list/tuple on left by an integer.
py: Implement floating point power binop.
Add a test.
py: Factor out static/class method unwrapping code; add tests.
Add more tests.
stmhal: Add backspace key to readline (along with delete key).
stmhal: Add timer module; move servo PWM from TIM2 to TIM5.

As per issue #257, servo is better on TIM5 because TIM2 is connected to
more GPIO.
Merge branch 'pip-micropy' of github.com:pfalcon/micropython into pfalcon-pip-micropy