Make d2i_X509 a generic d2i/i2d manpage.
Pull common stuff out of other d2i/i2d docs.
Update find-doc-nits to know about "generic" manpages.
Cleanup some overlap.
Fix up a bunch of other references.
Reviewed-by: Matt Caswell <matt@openssl.org>
Fix some code examples, trailing whitespace
Fix TBA sections in verify, remove others.
Remove empty sections
Use Mixed Case not ALL CAPS in head2
Enhance doc-nits script.
Remove extra =cut line
Reviewed-by: Richard Levitte <levitte@openssl.org>