Simple but functional timer control. More sophistication will
eventually be added, or for now just use direct register access :)
Also added pyb.freq() function to get MCU clock frequencies.
It's really a UART because there is no external clock line (and hence no
synchronous ability, at least in the implementation of this module).
USART should be reserved for a module that has "S"ynchronous capabilities.
Also, UART is shorter and easier to type :)
This is an attempt to clean up the Micro Python API on the pyboard.
Gpio functionality is now in the Pin object, which seems more natural.
Constants for MODE and PULL are now in pyb.Pin. Names of some
classes have been adjusted to conform to CamelCase. Other
miscellaneous changes and clean up here and there.
Pretty much everyone needs to include map.h, since it's such an integral
part of the Micro Python object implementation. Thus, the definitions
are now in obj.h instead. map.h is removed.
Can now choose at boot up whether the USB device is CDC+MSC or CDC+HID.
Choice is made by an option in boot.py, with default being CDC+MSC.
HID+MSC is not currently supported, but should be easy to implement.
Boot up now has ability to change the reset mode: hold down USR switch
while booting and LEDs will count from 1 to 7 to indicate the boot mode.
Release USR when correct mode is selected. Current modes are 1 (normal
boot), 2 (safe mode), 3 (reset FS mode).
