Add README.md target rule
0.04: Fixes for old pure-perl Scalar::Util

Warn in Makefile.PL about older pure-perl Scalar::Util.
require at least Scalar::Util 1.23

fix blessed call for old prototype, add parens.

improve docs (link to new perlhacktips/PERL_DESTRUCT_LEVEL)
mention the problem our variables, which are also destructed like
package variables (i.e. globals)

add -Mblib to external call in t/ogd02.t