Drift-compensated angle in gyro (#931)

* compute angle based on undrifted rate

* add is calibrating function

* fix integrator

* added example

* docs

* poll faster

docs/tutorials/drifter.md

@@ -0,0 +1,34 @@
+# Drifter
+
+Use this program to try out the gyro sensor and the effect of drifting.
+
+```typescript
+// this loop shows the rate, angle and drift of the robot
+forever(() => {
+    brick.showValue("rate", sensors.gyro2.rate(), 1)
+    brick.showValue("angle", sensors.gyro2.angle(), 2)
+    brick.showValue("drift", sensors.gyro2.drift(), 3)
+})
+// this loop shows wheter the sensor is calibrating
+forever(() => {
+    brick.showString(sensors.gyro2.isCalibrating() ? "calibrating..." : "", 4)
+})
+// instructions on how to use the buttons
+brick.showString("ENTER: calibrate", 7)
+brick.showString("       (reset+drift)", 8)
+brick.showString("LEFT: reset", 9)
+brick.showString("RIGHT: compute drift", 10)
+
+// enter -> calibrate
+brick.buttonEnter.onEvent(ButtonEvent.Pressed, function () {
+    sensors.gyro2.calibrate()
+})
+// right -> compute drift
+brick.buttonRight.onEvent(ButtonEvent.Pressed, function () {
+    sensors.gyro2.computeDrift()
+})
+// left -> reset
+brick.buttonLeft.onEvent(ButtonEvent.Pressed, function () {
+    sensors.gyro2.reset()
+})
+```

docs/tutorials/gyro.md

@@ -15,5 +15,11 @@
   "cardType": "tutorial",
   "url":"/tutorials/move-straight-with-gyro",
   "imageUrl":"/static/tutorials/move-straight-with-gyro.png"
+}, {
+  "name": "Drifter",
+  "description": "Explore how the gyro is drifting",
+  "cardType": "example",
+  "url":"/tutorials/drifter",
+  "imageUrl":"/static/tutorials/drifter.png"
 }]
 ```