opentype.js and paper.js should be external dependencies, not built-in

[louisremi]

Having those two libs built-in is problematic: we need to build opentype.js with a special command:

npm install derequire
browserify src/opentype.js --bare --standalone opentype | derequire > dist/opentype.js

It's convenient right now because we use forks of those libs (we have some pending PRs in both projects), but when they stabilize, we should probably consider using https://www.npmjs.com/package/browserify-global-shim

[louisremi]

No longer a problem, as we use pre-built versions of those packages, and no forks anymore.