Make anonymous enums follow Synopsis 2

Adding a pair to an enum is supposed to change the value the next key would get.

Before:

    enum ( a => 1, 'b' ).perl.say; # EnumMap.new("a", 1, "b", 0, )

Now:

    enum ( a => 1, 'b' ).perl.say; # EnumMap.new("a", 1, "b", 2, )