On start support (#324)

* annotating APIs to support onstart

* missed file

* updated templates

* adding new lines in main.ts

* fixing docs

* removing onstart

* updated docs

* updated various docs

* more docs

* adding upgrade policies for blocks

* updated pxt reference

* placing on start under "basic"

docs/blocks/logic/boolean.md

@@ -86,12 +86,14 @@ if (led.point(1,1) && led.point(2,2)) {
 When you compare two Numbers, you get a Boolean value, such as the comparison `x < 5` in the code below:
 
 ```blocks
-let x = Math.random(5)
-if(x < 5) {
-   basic.showString("low");
-} else { 
-   basic.showString("high");
-} 
+input.onButtonPressed(Button.A, () => {
+    let x = Math.random(5)
+    if(x < 5) {
+    basic.showString("low");
+    } else { 
+    basic.showString("high");
+    }
+})
 ```
 
 See the documentation on [Numbers](/reference/types/number) for more information on comparing two Numbers. You can also [compare strings](/reference/types/string-functions) using the `equals` function.

docs/blocks/logic/if.md

@@ -14,13 +14,15 @@ Click on the dark blue gear icon (see above) to add an *else* or *if* to the cur
 
 ### Example: adjusting screen brightness
 
-```blocks
-if(input.lightLevel()<100){
-    led.setBrightness(255);
-}
-```
+If the [light level](/reference/input/light-level) is `< 100`, this code sets the brightness to `255` when the button A is pressed:
 
-If the [light level](/reference/input/light-level) is `< 100`, this code sets the brightness to `255`:
+```blocks
+input.onButtonPressed(Button.A, () => {
+    if(input.lightLevel()<100){
+        led.setBrightness(255);
+    }
+})
+```
 
 ### See also