Update docs that currently use the depricated init option

[Madgvox]

Crossposting @webdesserts's issue:

As mentioned on stackflow, I ran into a few parts of the docs that still used the old init option over the new onrender option. I did a quick search through the docs and the following pages. Most of these are directly related to components.

• options (under components)
• partials
• components
• Ractive.extend()

[Rich-Harris]

All updated