snappybtn: new app. setWatch falling -> rising

Came out of this discussion: #3435

apps/snappybtn/ChangeLog

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+0.01: New App!

apps/snappybtn/README.md

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+# Snappy Button (BETA)
+
+Make your Bangle.js 2 watch react quicker when you press the hardware button.
+
+## Usage
+
+Just install it from the app loader to enable the behaviour on your watch.
+
+## Features
+
+The Bangle.js 2 often reacts at first when the hardware button is released. **Snappy Button** changes this so it reacts as soon as the button is pressed down.
+
+When installed the app highjacks the `setWatch` function and changes the `edge` option from `"falling"` to `"rising"`.
+
+Snappy button can be incompatible with some apps **(breaking them!)** that uses long presses of the hardware button. This is worked around by hardcoding Snappy Button to not interfere with these apps. **Please if you encounter problems report them as per below!**
+
+## TODO
+
+- Disable for more incompatible apps as they are found.
+- Enable for Bangle.js 1? **Help with testing needed!**
+
+## Requests
+
+Mention @thyttan in an issue on the espruino/BangleApps repository if you encounter problems or have an idea for improving Snappy Button.
+
+Pull requests always welcome!
+
+This app was proposed on the espruino/BangleApps repository: [Discussion: HW buttons should act on 'rising' edge](https://github.com/espruino/BangleApps/issues/3435) .
+
+## Creator
+
+gfwilliams, thyttan

apps/snappybtn/boot.js

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+{
+  let _setWatch = setWatch;
+  global.setWatch = (fn,pin,opt) => {
+    if (opt && opt.edge && opt.edge!="both" && global.__FILE__!="runplus.app.js") opt.edge = "rising";
+    return _setWatch(fn, pin, opt);
+  };
+}

apps/snappybtn/metadata.json

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+{ "id": "snappybtn",
+  "name": "Snappy Button (BETA)",
+  "version":"0.01",
+  "description": "Make your Bangle.js 2 watch react quicker when you press the hardware button. This is an **experimental or BETA** app.",
+  "icon": "app.png",
+  "tags": "ui,interface,ux,faster,quicker,shorter,speed",
+  "type": "bootloader",
+  "supports" : ["BANGLEJS2"],
+  "readme": "README.md",
+  "storage": [
+    {"name":"snappybtn.boot.js","url":"boot.js"}
+  ]
+}