updated AS:Callbacks doc for terminator option in define_callbacks method
The change is commited at ba552764344bc0a3c25b8576ec11f127ceaa16da
unified the param names across all callbacks manipulation methods
_ Rename the define_callbacks params to `names`
  - in order to match the naming conventions for `get_callbacks` and `set_callbacks` at https://github.com/rails/rails/blob/master/activesupport/lib/active_support/callbacks.rb#L736-743
  - `define_callbacks` just register names(events), not define the real callback functions.
- Rename the `reset_callbacks` params
Merge pull request #11195 from yangchenyun/update_doc_for_define_callbacks

updated AS:Callbacks docs, variable namings