Adding Approx files.

I'm not sure what state they are in though.
Updated Smten.v to use empty, single, union, map, and join.

Instead of return, zero, plus, and bind.
Updated SmtenProp to use updated Smten syntax.
Updated SmtenS1 with changes in Smten syntax.
Updated SmtenS with updated Smten syntax.
Updated SmtenIO with updates to Smten syntax.
Re-organized repository and added a README file.