Fix compile warnings

Fix compile warnings on release 17

src/bertconf.erl:11: opaque type version() is not exported

Makes me nervous, considering the warning:
%% The version is the table id, which should be swapped on
%% any update. This is a very scary thing to use, but it works
%% as long as we use it as an opaque data type.
But it passes it's tests... 

src/bertconf_lib.erl:31: crypto:md5/1 is deprecated and will be removed in in a future release; use crypto:hash/2