v0.4.1

What's Changed

This includes a breaking change, but it should have been included in the 0.4.0, so releasing this as a minor.

• Update readme in #31
• Only call .onchange for change events in #32
• [dispatchEvent] check argument in #33
• [test][onchange] add test case for once in #34

Full Changelog: v0.4.0...v0.4.1