add html5 input type `number` support

[peppertom]

Added <input type="number"> support.

refs: #43

[wolfika]

Hi @peppertom, thanks for the effort, this is a great addition! As a general advice on open source contributions however, please don't make code style and indentation changes in the same commit as your actual change, because it renders the diff view unusable, and your actual meaningful changes to the logic get lost. In fact, don't make code style changes without first discussing it with the project's maintainers.