Unicode Set version 0.7.0

Enhancements

• Add Unicode.Set.character_class/1 which returns a string compatible with Regex.compile/2. This supports the idea of expanded Unicode Sets being used in standard Elixir/erlang regular expressions and will underpin implementation of Unicode Transforms in the package unicode_transform

• Add Unicode.Regex.compile/2 to pre-process a regex to expand Unicode Sets and the compile it with Regex.compile/2. Unicode.Regex.compile!/2 is also added.