Data attributes are only pulled in at initialization about wiv.js

[bendemeyer]

This should be doable: https://stackoverflow.com/questions/41424989/javascript-listen-for-attribute-change

Relevant docs: https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver

[bendemeyer]

Simple implementation here, not opening a PR yet because it includes some other not-yet-merged changes: bendemeyer@56914a3

Note that this refreshes all the attribute-based cache fields for a given wiv when any attribute change takes place. This could be addressed in the future if that optimization seems worthwhile.

Also, potentially a bigger concern, editing the height or thickness attributes will cause the wiggles to adjust accordingly, but will not resize the canvas or the content elements. The fix for this would be to factor the sizing of those elements into a specific function, then work our way up the DOM tree calling it for every wiv we encounter.

[jjkaufman]

@bendemeyer everything looks good, including the resizing 😀