add an opaque Text type to the language standard

[GregWeber]

Add the Text datatype to the language.

The text package for GHC exposes a Text datatype that represents a string.

The current String = [Char] standard has issues with

• efficiency: there are more efficient representations than linked lists
• correctness: for Unicode correctness, one must operate on a string as a whole rather than individual code points

see OpaqueText