Change generic JavaScript `Error` object to more specific
`TypeError`:

- https://nodejs.org/api/errors.html#errors_class_typeerror
- https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError

The HTML to DOM parser has been externalized to its own package.

Save to dependencies:
- html-dom-parser@0.0.2

Remove from dependencies:
- domhandler@2.3.0
- htmlparser2@3.9.1

Remove files:
- lib/html-to-dom-server.js
- lib/html-to-dom-client.js

Update `index.js` to require `html-dom-parser`.

Fix broken requires in tests now that `lib/html-to-dom-server.js`
and `lib/html-to-dom-client.js` have been deleted (use
`html-dom-parser` instead).

Remove HTML to DOM tests since `html-dom-parser` has its own tests.

Remove `helpers.deepEqualCircular()` and its tests as it was
used to test HTML to DOM parsing (which is no longer handled by
this package, but `html-dom-parser`).

- Rename `test/data.json` to `test/helpers/mocks.json`
- Require mocks in test helpers index
- Add a test for doctype (should be skipped and not parsed)
- Tidy tests

Replace `htmlparser2` with `html-dom-parser` link and tidy up
other parts.

Replace HTML to DOM implementation with `html-dom-parser` package

- Replace HTML to DOM implementation with `html-dom-parser` (#28)
  - Update dependencies
    - Save `html-dom-parser`
    - Remove `domhandler` and `htmlparser2`
  - Update tests
    - Remove unused tests and helpers
    - Update mocks
    - Add test for doctype
- Throw `TypeError` instead of `Error` for invalid first argument
  - Update tests
- README
  - Update "Special Thanks" section
  - Tidy where necessary