handleChange parses value twice

[martijnvermaat]

I think values are parsed twice in the handleChange handlers, since the parser is also called in the normalizer.

See this handler for example.

[odf]

Thanks for bringing that to my attention! Since normalizing and parsing are always done together, it might make more sense to have a single function that returns both the normalized text and the parsed value, if any.

We now have a bit of duplication between the input components, and more so after considering #18, so I think I should look into further refactoring some of that code. But first it's probably a good idea for me to sort out testing.