added input.onPinRelease. Fix for #294

docs/reference/input/on-pin-released.md

@@ -0,0 +1,48 @@
+# On Pin Released
+
+Start an [event handler](/reference/event-handler) (part of the
+program that will run when something happens, like when a button is
+pressed).  This handler works when you release pin `0`, `1`, or `2`
+together with `GND`.  When you are using this function in a web
+browser, click and release the pins on the screen instead of the ones on the BBC
+micro:bit.
+
+If you hold the `GND` pin with one hand and touch pin `0`, `1`, or `2`
+with the other, a very small (safe) amount of electricity will flow
+through your body and back into the micro:bit. This is called
+**completing a circuit**. It's like you're a big wire!
+
+```sig
+input.onPinReleased(TouchPin.P0, () => {
+})
+```
+
+## ~hint
+
+This function works best when the BBC micro:bit is using batteries for power,
+instead of the USB cable.
+
+## ~
+
+## Parameters
+
+* ``name`` means the pin that is being released, either `P0`, `P1`, or `P2`
+
+### Example: pin pressed counter
+
+This program counts how many times you release the `P0` pin. 
+Every time you release the pin, the program shows the number of times on the screen.
+
+```blocks
+let count = 0
+basic.showNumber(count, 100)
+input.onPinReleased(TouchPin.P0, () => {
+    count = count + 1
+    basic.showNumber(count, 100)
+})
+```
+
+### See also
+
+[BBC micro:bit pins](/device/pins), [pin is pressed](/reference/input/pin-is-pressed), [analog read pin](/reference/pins/analog-read-pin), [analog write pin](/reference/pins/analog-write-pin), [digital read pin](/reference/pins/digital-read-pin), [digital write pin](/reference/pins/digital-write-pin)
+