Support web browsers #2

Although the project is mainly targeted to Deno as of now, it is open to expand its target runtimes including web browsers in particular. There would be subtasks to let it support web browsers:

• Compatibility. The current implementation probably depends on several APIs which are unavailable on web browsers. These should be rewritten in the more portable and standard way.
• Unit tests. Currently the unit tests are based on Deno's built-in testing framework. The unit tests should be possible to run on all supported runtimes.
• Packaging. Although Deno uses ESM by default, as the entire source code is written in TypeScript, it still needs to be compiled to JavaScript, and preferably, bundled into a single .jsm file so that users can use it using <script type=module> tag.
• CI. Everything above needs to be continuously integrated and delivered.