[S02] define .Stringy and .gist for Num and Rat

leave a bit of wiggle room in the Num stringification fow now.

S02-bits.pod

@@ -775,7 +775,11 @@ calculation, with the same result on decimal-normalizable fractions,
 but where C<.perl> would produce the C<-47/3> form, stringification instead
 converts to C<Num> and stringifies that, so the rational internal form is
 somewhat hidden from the casual user, who would generally prefer
-to see pure decimal notation.
+to see pure decimal notation. C<Rat.gist> follows the same rules as
+stringification.
+
+C<Num.Str> and C<Num.gist> both produce valid Num literals, so they must
+include the C<e> for the exponential.
 
     say 1/5;    # 0.2 exactly (not via Num)
     say 1/3;    # 0.333333333333333 via Num
@@ -794,6 +798,7 @@ to see pure decimal notation.
 
     say <555555555555555555555555555555555555555555555/5>.perl
                 # 111111111111111111111111111111111111111111111/1
+    say 2e2;    # 200e0 or 2e2 or 200.0e0 or 2.0e2
 
 =head2 Infinity and C<NaN>