Fix issues

[chpio]

Hi,

this PR changes:

• fixes TS declarations. The old one took a undefined | string as initialValue but returned string, which is wrong.
• removes initialValue
• fixes hydration mismatch between SSR & browser rendering
• rewrites the js code to ts (no need to maintain separate TS declarations)

issues:

• What are reasonable return values for the hook?: initialValue doesn't actually set cookie #16 (comment)

  1. the first render = `null`?
  2. there's no cookie = `undefined`?
  

• the usage of the hook in multiple components might cause changes in one comp to not be reflected in the other comps If more than one component uses the same cookie, update all of those components when cookie value is set in one of them #15
• not really tested

[chpio]

1. seems there's no interest in this
2. i guess it's because it changes to much? going to need to release my own fork.

edit: i was waiting/hoping for some inputs here or in #16