CRM_Utils_Hook_Inspector - Add util for displaying hook metadata

CRM_Utils_Hook_Inspector - Add util for displaying hook metadata

This is meant to facilitate better code-generators and
documentation-generators. Key features:

 * Adds a new class, `CRM_Utils_Hook_Inspector`.
 * Adds a new hook, `hook_civicrm_hooks`. Extensions may use this to document their hooks.
 * Implements the hook in core (to report on `civicrm-core` hooks)
 * If you follow the practice of declaring static hook stubs (like
   `civicrm-core` does), then use `addStaticStubs()` to assimilate of them.