Make changes to support HitL testing.

- Rename all examples so that they have underscores instead of hyphens. .py
files with hyphens in their names can't be imported.
- Add a test/hitl/ directory with one test (so far): cpy_test.py. This test
makes sure that cpy_example.py runs successfully on a CircuitPython host
connected to a Notecard. I tested using a Notecarrier F and a Swan.
- cpy_test.py relies on pyboard.py from MicroPython. I have added that file
from MicroPython's master branch here.

Author: haydenroche5

README.md

@@ -136,11 +136,11 @@ The documentation for this library can be found
 The [examples](examples/) directory contains examples for using this
 library with:
 
-- [Serial](examples/notecard-basics/serial-example.py)
-- [I2C](examples/notecard-basics/i2c-example.py)
-- [RaspberryPi](examples/notecard-basics/rpi-example.py)
-- [CircuitPython](examples/notecard-basics/cpy-example.py)
-- [MicroPython](examples/notecard-basics/mpy-example.py)
+- [Serial](examples/notecard-basics/serial_example.py)
+- [I2C](examples/notecard-basics/i2c_example.py)
+- [RaspberryPi](examples/notecard-basics/rpi_example.py)
+- [CircuitPython](examples/notecard-basics/cpy_example.py)
+- [MicroPython](examples/notecard-basics/mpy_example.py)
 
 ## Contributing