Add announcer script

I always keep writing up this same announcement message whenever I publish a new version.

I've now written a script to automate my announcement formatting, it looks like this:

```
**MetaMask 2.13.2** now published to the Chrome Store! It should be available over the next hour!
 2016-10-4

- Fix bug where chosen FIAT exchange rate does no persist when switching networks
- Fix additional parameters that made MetaMask sometimes receive errors from Parity.
- Fix bug where invalid transactions would still open the MetaMask popup.
```

development/announcer.js

@@ -0,0 +1,12 @@
+var manifest = require('../app/manifest.json')
+var version = manifest.version
+
+var fs = require('fs')
+var path = require('path')
+var changelog = fs.readFileSync(path.join(__dirname, '..', 'CHANGELOG.md')).toString()
+
+var log = changelog.split(version)[1].split('##')[0].trim()
+
+let msg = `**MetaMask ${version}** now published to the Chrome Store! It should be available over the next hour!\n${log}`
+
+console.log(msg)

package.json

@@ -15,7 +15,8 @@
     "mock": "beefy mock-dev.js:bundle.js --live --open --index=./development/index.html --cwd ./",
     "buildMock": "browserify ./mock-dev.js -o ./development/bundle.js",
     "testem": "npm run buildMock && testem",
-    "ci": "npm run buildMock && testem ci -P 2"
+    "ci": "npm run buildMock && testem ci -P 2",
+    "announce": "node development/announcer.js"
   },
   "browserify": {
     "transform": [