Fix usart_obj_tx_str

* Fix usart_obj_tx_str to send the actual string.
* Fix issue #126

dict views now, refactoring later.

Add USART Micro Python Bindings

Implement str.strip

Count individual testcases when running tests.

Creating of classes (types) and instances is much more like CPython now.
You can use "type('name', (), {...})" to create classes.

* Add a DEBUG flag to Makefile, enables: "-O0 -ggdb"

* Add Micro Python bindings to usart.c
* Export USART python object to namespace pyb

The idea is simple: each print represents a testcase within a test unit.
As we don't have strict rules on which/how many testcase are put into
a test file, it's nice to have an idea how many *testcases* we have
totally. Would be nice to count how many testcases pass/fail, but
that's a bit less trivial.

Use computed string to exercise string interning code better.

Make build output quieter.

Use make V=1e make V=1 or set BUILD_VERBOSE in your environment to increase build verbosity.

This should fix issue #117

Addresses issue #104.

Define buffer and stream protocols, and other starting bits of io.* framework, with io.FileIO-like implementation for Unix

Update teemsy/Makefile to use py.mk

Update stm/Makeile to use OBJCOPY and SIZE macros

I also fixed main.c to compile with the new str lexer

While updating the teensy Makfile, I noticed that the stm Makefile
was using calling arm-none-eabi-objcopy and size rather than
$(OBJCOPY) and $(SIZE), so I added these 2 for consistency.

Note: only read/write/close methods are defined so far, and class
is not exposed (use open() factory function, as usual).

These can be used for any object which implements stream protocol
(mp_stream_p_t).

Stream protocol is abstraction of serial I/O. Buffer protocol is
abstraction of random-access I/O. These protocols are defined down
to C level, to allow generic, while still efficient algorithms
to be coded in C (like, buffered transfer between 2 stream objects,
saving/loading of buffer object to/from stream, etc). (Note that CPython
define buffer protocol on C level, but apparently not stream protocol).

Use LSI OSC for RTC clock when LSE is not detected

Updated teensy to use common code from stm directory.

* Fix rtc_init to use LSI for RTC clock source when LSE is not detected.

Updated mconfigport.h to enable GC

Dictionary features that don't involve views or classmethods. First part of issue #99.