Doc nits: callback function typedefs

Enhance find-doc-nits to be better about finding typedefs for
callback functions.  Fix all nits it now finds.  Added some new
typedef names to ssl.h some of which were documented but did not
exist

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2151)
(cherry picked from commit 121677b4)