First stab at writing tests.

Setup npm package.json with mocha, sinon, chai and lodash as dev dependencies.

Wrote test for salsa20.js.

Added boilerplate to salsa20.js to expose it to module loaders.
Added more Sals20 tests.

Better refactor of salsa20.js as modular code.
'window' object not available inside web workers - use 'this' instead.