Add game 'life' api reference (#1569)

docs/reference/game/add-life.md

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+# add Life
+
+Increase the number of lives remaining by some amount.
+
+```sig
+game.addLife(0)
+```
+
+The life count in the game is increased by the number of lives you say.
+
+## Parameters
+
+* **life**: a [number](/types/number) to remove from the count.
+
+## Example #example
+
+Add `20` more lives to the life count if the player's score reaches `10000` points.
+
+```blocks
+let giveLives = true
+
+if (game.score() > 9999) {
+    if (giveLives) {
+        game.addLife(20)
+        giveLives = false
+    }
+}
+```
+
+## See also #seealso
+
+[set life](/reference/game/set-life),
+[remove life](/reference/game/remove-life)

docs/reference/game/remove-life.md

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+# remove Life
+
+Decrease the number of lives remaining by some amount.
+
+```sig
+game.removeLife(0)
+```
+
+The life count in the game is decreased by the number of lives you say. If the life count reaches `0` when these lives are removed, then the game is over.
+
+## Parameters
+
+* **life**: a [number](/types/number) to remove from the count.
+
+## Example #example
+
+Take away `20` lives count if the player's score reaches `10000` points.
+
+```blocks
+let giveLives = true
+
+if (game.score() > 9999) {
+    if (giveLives) {
+        game.removeLife(20)
+        giveLives = false
+    }
+}
+```
+
+## See also #seealso
+
+[set life](/reference/game/set-life),
+[add life](/reference/game/add-life)

docs/reference/game/set-life.md

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+# set Life
+
+Set the game life count to this amount.
+
+```sig
+game.setLife(0)
+```
+
+Your program has a life counter which you can set to record the number of lives remaining for a player in your game. If you set the life count to `0` or less, the game ends.
+
+## Parameters
+
+* **value**: a [number](/types/number) to set the life count to.
+
+## Example #example
+
+Set the player life count to `9` lives before starting the game.
+
+```blocks
+game.setLife(9)
+```
+
+## See also #seealso
+
+[add life](/reference/game/add-life),
+[remove life](/reference/game/remove-life)