Prevent keyboard modifier events from scrolling down

[Tyriar]

Fixes #363

---

Notes:

• This is the first TypeScript file
• I'm suggesting a new format for .ts test files so they lay right next to the source file they're testing, this prevents duplicating the directory structure under the test/ dir
• The new @types dependencies provide type information for mocha and chai, allowing TypeScript to check the types when compiling. From TS 2 this is as easy as running npm i -D @types/mocha

[parisk]

I am totally 👍 for the new test file format. Sounds much more sane.