- Link to Deprecation::Behavior in configuring guide

  The current list of options for `config.active_support.deprecation`
  was missing the newly added `:report` option. Instead of adding the
  missing option and continuing to keep 4 different lists of the same
  options in sync, I opted to replace the list with a link to the
  options in the Behavior API docs. This had the additional advantage of
  giving more information about all of the options which was not
  mentioned in the Configuring guide.

- Use symbols for Behavior options

  It felt to me like naming the options did not make it explicit that
  those were the symbols to pass to `#behavior=`, but by adding the `:`
  that becomes more clear.

- Add some API links

  There were a few references to `behavior=`, but we may as well link to
  the actual method.