fixed Microphone example

[georgcampana]

• read reducesd to 256 samples (instead of 1024) since only 160 are displayed
• added a Gain factor to amplify the signal before displaying
• adcBuffer is a buffer of 16bit signed integers (not unsigned)
• map is now mapping correctly the signed value (from MIN16 to MAX16)
• i2s_read_bytes() is deprecated: replaced with i2s_read()
• main task loop is now waiting 1 sec at a time to not race-run wasting cpu cycles
• no need to stick the audio read task to a particular core: replaced xTaskCreatePinnedToCore() with xTaskCreate()
• the "oldx" vector is completely useless, it would always contain the index number.

[EeeeBin]

thanks :)