Include pico_tone library

[jcarranz97]

Fixes #69 This PR was previously made against pico-sdk but now requesting to include the library as part of pico-extras as per @lurch recommendation.

This PR includes tone functions to generate tones using PWM.

The tone function is similar to tone() from Arduino. I have also included a no_tone function to silence buzzer if needed.

Inspiration and References:

• [docs.arduino.cc] - Play a Melody using the tone() function
• [www.hackster.io] - PWM Sound Synthesis
• [peppe8o.com] - Passive Buzzer with Raspberry PI Pico and MicroPython