Replace calls to the global `$core` variable with `$this->core` where possible.
Add an extra blank line for readability.
Add extra sanity checks.
Move the space outside the anchor tag.
Add the breadcrumb to the admin page.
Conform the name of the admin REST class to the others.
Increase the maxmimum length of the tooltips.
Display a confirmation message when the settings have been updated.
Bump to v0.3.0.