[S05] add :r alias for :ratchet

std, rakudo and niecza already support it anyway

Author: moritz

S05-regex.pod

@@ -213,6 +213,7 @@ The single-character modifiers also have longer versions:
          :i        :ignorecase
          :m        :ignoremark
          :g        :global
+         :r        :ratchet
 
 =item *
 
@@ -546,7 +547,7 @@ not a (presumably immutable) string value.]
 
 =item *
 
-The new C<:ratchet> modifier causes this regex to not backtrack by default.
+The new C<:r> or C<:ratchet> modifier causes this regex to not backtrack by default.
 (Generally you do not use this modifier directly, since it's implied by
 C<token> and C<rule> declarations.)  The effect of this modifier is
 to imply a C<:> after every atom, including but not limited to