Add CharSets/CharShortMaps utilities/views

[leventov]

net.openhft.collect.CharSets {
  CharSet empty(); // immutable
  CharSet singleton(char e); // immutable
  CharCollection asImmutable(Collection<Character> )
}

net.openhft.collect.map.CharShortMaps {
  CharShortMap emptyMap(); // immutable
  asImmutableMap(char[] keys, char[] values);
  asImmutable(Map<Character, Short> map);
}

Or something like this