docs/machine.Timer: Move WiPy adhoc parts to its documentation.

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+Hardware timers
+===============
+
+Timers can be used for a great variety of tasks, calling a function periodically,
+counting events, and generating a PWM signal are among the most common use cases.
+Each timer consists of two 16-bit channels and this channels can be tied together to
+form one 32-bit timer. The operating mode needs to be configured per timer, but then
+the period (or the frequency) can be independently configured on each channel. 
+By using the callback method, the timer event can call a Python function.
+
+Example usage to toggle an LED at a fixed frequency::
+
+    from machine import Timer
+    from machine import Pin
+    led = Pin('GP16', mode=Pin.OUT)                  # enable GP16 as output to drive the LED
+    tim = Timer(3)                                   # create a timer object using timer 3
+    tim.init(mode=Timer.PERIODIC)                    # initialize it in periodic mode
+    tim_ch = tim.channel(Timer.A, freq=5)            # configure channel A at a frequency of 5Hz
+    tim_ch.irq(handler=lambda t:led.toggle(), trigger=Timer.TIMEOUT)        # toggle a LED on every cycle of the timer
+
+Example using named function for the callback::
+
+    from machine import Timer
+    from machine import Pin
+    tim = Timer(1, mode=Timer.PERIODIC, width=32)
+    tim_a = tim.channel(Timer.A | Timer.B, freq=1)   # 1 Hz frequency requires a 32 bit timer
+
+    led = Pin('GP16', mode=Pin.OUT) # enable GP16 as output to drive the LED
+
+    def tick(timer):                # we will receive the timer object when being called
+        global led
+        led.toggle()                # toggle the LED
+
+    tim_a.irq(handler=tick, trigger=Timer.TIMEOUT)         # create the interrupt
+
+Further examples::
+
+    from machine import Timer
+    tim1 = Timer(1, mode=Timer.ONE_SHOT)                               # initialize it in one shot mode
+    tim2 = Timer(2, mode=Timer.PWM)                                    # initialize it in PWM mode
+    tim1_ch = tim1.channel(Timer.A, freq=10, polarity=Timer.POSITIVE)  # start the event counter with a frequency of 10Hz and triggered by positive edges
+    tim2_ch = tim2.channel(Timer.B, freq=10000, duty_cycle=5000)       # start the PWM on channel B with a 50% duty cycle
+    tim2_ch.freq(20)                                                   # set the frequency (can also get)
+    tim2_ch.duty_cycle(3010)                                           # set the duty cycle to 30.1% (can also get)
+    tim2_ch.duty_cycle(3020, Timer.NEGATIVE)                           # set the duty cycle to 30.2% and change the polarity to negative
+    tim2_ch.period(2000000)                                            # change the period to 2 seconds
+
+
+Additional constants for Timer class
+------------------------------------
+
+.. data:: Timer.PWM
+
+   PWM timer operating mode.
+
+.. data:: Timer.A
+.. data:: Timer.B
+
+   Selects the timer channel. Must be ORed (``Timer.A`` | ``Timer.B``) when
+   using a 32-bit timer.
+
+.. data:: Timer.POSITIVE
+.. data:: Timer.NEGATIVE
+
+   Timer channel polarity selection (only relevant in PWM mode).
+
+.. data:: Timer.TIMEOUT
+.. data:: Timer.MATCH
+
+   Timer channel IRQ triggers.