Read perlunicode. You can use names for unicode characters and pick them out of a list to get the substitutions you want. The list also has the numeric codes if you prefer to do it that way.

use charnames ":full";

$string =~ s{ 
              \N{LEFT SINGLE QUOTATION MARK} | \N{RIGHT SINGLE QUOTATI
+ON MARK} 
            }
            {
              \N{APOSTROPHE} 
            }xg;
[download]

You may also get some mileage out of these properties, but the caveat from perlunicode would make me a bit nervous.

    Pi          InitialPunctuation
                (may behave like Ps or Pe depending on usage)
    Pf          FinalPunctuation
                (may behave like Ps or Pe depending on usage)
[download]

(And yes, a module to do this translation automatically would be very nice!)