* Unified the surface syntax. There are no longer distinctions between
single-arity and multi-arity function/function types.
* Removed case and case*, in favor of match, a single advanced pattern
matching construct.
* Updated all libraries, tests and documentation to use these new syntax.
* Some work to provide improved error messages in surface syntax.
Created split packages: cur, cur-lib, cur-test, cur-doc, similar to
other Racket packages, e.g., redex.
* Moved tests out of core and into cur-test
* Moved docs into cur-doc
* Moved cur implementation and libraries into cur-lib
* Added cur meta-pacakge that installs all of the above
