This PR makes r2wc treat prop declared as "boolean" , i.e.

const SomeElement = r2wc(Some, {
  props: {
    foo: "boolean"
  }
})

with reasonable portion of semantics of HTML Boolean attribute (as described in https://developer.mozilla.org/en-US/docs/Glossary/Boolean/HTML) so it's still as backwards compatible as possible.

If an HTML tag contains a boolean attribute - no matter the value of that attribute - the attribute is set to true on that element.

specified part is deliberately not obeyed by code I propose, as pre-existing behavior is very much different. With this PR values that were considered false before (e.g. 0, no, false, n, f, etc.) are still considered false

If an HTML tag does not contain the attribute, the attribute is set to false.

If the attribute is present, it can have one of the following values:

• no value at all, e.g. attribute
• the empty string, e.g. attribute=""
• attribute's name itself, with no leading or trailing whitespace, e.g. attribute="attribute"

this part is AFAIK followed faithfully.

This one also borrows some ideas from unfinished #123 by @shoumaw (handling booleans before running transform.parse, but not the deprecation of syntax defined as ^[ty1-9]).
In fact: I ensured the current behavior with more tests - until it's actually decided that it should be dropped, I think it's worth having it secured

Fixes #162