Use proper documentation tags

git_cred_acquire_cb isn't using the standard @param and @return tags.
This is causing the generated documentation to not be formatted
properly.

include/git2/transport.h

@@ -321,13 +321,13 @@ GIT_EXTERN(void) git_cred_free(git_cred *cred);
 /**
  * Signature of a function which acquires a credential object.
  *
- * - cred: The newly created credential object.
- * - url: The resource for which we are demanding a credential.
- * - username_from_url: The username that was embedded in a "user\@host"
+ * @param cred The newly created credential object.
+ * @param url The resource for which we are demanding a credential.
+ * @param username_from_url The username that was embedded in a "user\@host"
  *                          remote url, or NULL if not included.
- * - allowed_types: A bitmask stating which cred types are OK to return.
- * - payload: The payload provided when specifying this callback.
- * - returns 0 for success, < 0 to indicate an error, > 0 to indicate
+ * @param allowed_types A bitmask stating which cred types are OK to return.
+ * @param payload The payload provided when specifying this callback.
+ * @return 0 for success, < 0 to indicate an error, > 0 to indicate
  *       no credential was acquired
  */
 typedef int (*git_cred_acquire_cb)(