Redirect theme and plugin editor function reference to developer.wordpress.org

[netweb]

Currently the theme and plugin editor function lookups link to ​http://phpdoc.wordpress.org/, these should link to the new code reference at ​https://developer.wordpress.org.

Via ​http://codex.wordpress.org/WordPress.org_API#Editor

https://api.wordpress.org/core/handbook/1.0/?function={function}&version={wp-version}&redirect=true

e.g. A lookup of register_activation_hook from a plugin is currently redirecting to ​http://phpdoc.wordpress.org/trunk/WordPress/Plugin/_wp-includes---plugin.php.html#functionregister_activation_hook

This is the same page as ​http://phpdoc.wordpress.org/ because all other links either no longer exist or are blocked e.g. ​http://phpdoc.wordpress.org/trunk/ and return 403 Forbidden

[nacin]

There is nothing worth keeping in the code for that handbook endpoint, so it'll need to be new (and open sourced).

Things to keep in mind:

• Check get_defined_functions() for internal functions and send them off to php.net instead.
• Redirect them to developer.wordpress.org otherwise.
• If a function doesn't exist for whatever reason, developer.wordpress.org needs a half-decent 404 page.
• If $redirect is false, then a simple echo of the target URL occurs.
• Locale is received but nothing happens with it.
• Version is received but nothing will happen with it.

[ocean90]

Duplicate of #426.