fix: export Drift's public API

[frederickfogerty]

Description

This PR uses the approach preferred by the Closure docs to export the public API of the Drift class. This has to happen because Closure rewrites the names of the class methods, which prevents third-parties from calling methods by their proper names.

Fixes #81

Bug Fix

• All existing unit tests are still passing (if applicable)
• [N/A] Add new passing unit tests to cover the code introduced by your PR
• [N/A] Update the readme
• [N/A] Update or add any necessary API documentation
• Add some steps so we can test your bug fix
• The PR title is in the conventional commit format: e.g. fix(<area>): fixed bug #issue-number
• Add your info to the contributors array in package.json!

Steps to Test

Steps:

1. Clone this PR, npm install
2. Run npm run build:watch
3. Play around with drift in index.html. console.log(new Drift(...)) should show that everything is exported on the prototype.