Generate friend initiation hook dynamically.

This makes it easier to document per WP standards.

Props tw2113.
See #5942.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9173 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
Add hook documentation in bp-friends-functions.php.

Props tw2113.
See #5942.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9174 cdf35c40-ae34-48e0-9cc9-0c9da1808c22