Consider renaming example to match standards

[kattni]

Example is currently named boardtest_suite.py. Consider renaming it to boardtest_simpletest.py to match the CircuitPython library standards.

The lines including this file name in the docs/examples.rst file must also be updated to reflect the name change, e.g.:

.. literalinclude:: ../examples/current_file_name.py
    :caption: examples/current_file_name.py
    :linenos:

would be updated to:

.. literalinclude:: ../examples/current_file_name_changed.py
    :caption: examples/current_file_name_changed.py
    :linenos: