docs: Cleanup and update some docs.

docs/library/cmath.rst

docs/library/gc.rst

docs/library/math.rst

docs/library/os.rst

docs/library/pyb.ADC.rst

docs/library/pyb.Accel.rst

docs/library/pyb.CAN.rst

docs/library/pyb.DAC.rst

docs/library/pyb.ExtInt.rst

docs/library/pyb.I2C.rst

docs/library/pyb.LCD.rst

docs/library/pyb.LED.rst

docs/library/pyb.Pin.rst

docs/library/pyb.PinAF.rst

docs/library/pyb.RTC.rst

docs/library/pyb.SPI.rst

docs/library/pyb.Servo.rst

docs/library/pyb.Switch.rst

docs/library/pyb.Timer.rst

docs/library/pyb.UART.rst