tone: Work with 4.x, 5.0; AudioOut and PWMAudioOut

[jepler]

.. by creating new private functions for getting the right AudioOut and RawSample objects.

INCOMPATIBLE CHANGE: this removes support for CircuitPython versions before 3.x in tone()

Testing performed: On CPB, tone(board.SPEAKER, 440). On Metro M4 Express, `tone(board.A0, 440). Both tests were using CircuitPython 5.0.alpha versions.

Closes: #45

[kattni]

Tested on Circuit Playground Bluefruit with demo code from CircuitPython Essentials PWM guide page. Plays one tone, and then fails with pin in use, regardless of pin used. Tried with board.SPEAKER and board.A2 for use with piezo.

[jepler]

I expect to discover that the "pin in use" error is a problem in core, but I am still chasing it down, because I didn't make it happen without using simpleio yet. I did reproduce it with kattni's script and the code in this pull request, though:

import time
import board
import simpleio

while True:
    for f in (262, 294, 330, 349, 392, 440, 494, 523):
        # For the M0 boards:
        simpleio.tone(board.A2, f, 0.25)  # on for 1/4 second
        # For the M4 boards:
        # simpleio.tone(board.A1, f, 0.25)  # on for 1/4 second
        time.sleep(0.05)  # pause between notes
    time.sleep(0.5)

[jepler]

The problem that @kattni encountered is in core and has been filed as adafruit/circuitpython#2146 with proposed fix at adafruit/circuitpython#2147 -- but testing of this issue on CPB or other nRF boards will depend on using firmware with that fixed.

[ladyada]

please verify it on a CPX with 4.x as well as 5.x :)

[kattni]

Verified that change works on CPX with 4.x and 5.x.

[tannewt]

Thanks for doing this. Ideally we'd limit use of try/except for this.

[tannewt]

Looks better! Thank you!