Add time.mktime and enhance time.localtime (for stmhal)

Now you can use time.localtime on the timestamps presented by os.stat
stmhal, modtime: Small changes, reduced code size by around 80 bytes.

Also added test for modtime.
Merge branch 'dhylands-localtime'
Added python script to map AF to a pin name

Added some functions to Pin class to query mode, pull, and af
stmhal, pin: Update documentation.
examples: Added pins.py example script to list pin config/af.

Script is due to Dave Hylands.
py: Consolidate min/max functions into one, and add key= argument.

Addresses issue #811.
Add save/restore_irq

Factored irq functions into a separate file.
stmhal: Make enable_irq and disable_irq inline functions.

These functions are generally 1 machine instruction, and are used in
critical code, so makes sense to have them inline.

Also leave these functions uninverted (ie 0 means enable, 1 means
disable) and provide macro constants if you really need to distinguish
the states.  This makes for smaller code as well (combined with
inlining).

Applied to teensy port as well.
Add save/restore_irq

Factored irq functions into a separate file.
Add support for pyb.micros() by using the systick timer.

I also removed trailing spaces from modpyb.c which affected a couple
of lines technically not part of this patch.

Tested using: https://github.com/dhylands/upy-examples/blob/master/micros_test.py

which eventually fails due to wraparound issues (I could fix the test to compensate
but didn't bother)
stmhal: Use MP_OBJ_NEW_SMALL_INT directly in pyb.micros/millis.

Also some whitespace cleanup.
teensy: Fix multiple definition of irq functions.
stmhal: Improve efficiency of SysTick IRQ and HAL_Delay.

SysTick IRQ now increases millisecond counter directly (ie without
calling HAL_IncTick).  Provide our own version of HAL_Delay that does a
wfi while waiting.  This more than halves power consumption when running
a loop containing a pyb.delay call.  It used to be like this, but new
version of HAL library regressed this feature.
Fix sdcard_power_on to not do anything if the card is already powered on.
tests: Add test for pyb.disable_irq and pyb.enable_irq.
py: Add dispatch for user defined ==, >, <=, >=.

Addresses issue #827.
stmhal: Fix build issues with (old) CC3000 driver.

Addresses issue #825.
stmhal: Hookup USB_VCP.any().

Thanks to Dave Hylands for this patch.
Add pip-micropython to unix make install.

Also add -t/--target option to pip-micropython to allowing installing to
the pyboard.

Thanks to turbinenreiter/Sebastian Plamauer for the patch.