Create dev-1.0.0 branch

[prushforth]

In theory:

• create a branch for 1.0.0 development -> dev-1.0.0
• populate with custom element boilerplate for all existing elements
• migrate functionality from existing code into new custom elements
• get tests working
• update documentation
• merge into main
• release 1.0.0

[prushforth]

We're going to take this one element at a time, no need for a dev branch.