These macros were not really serving a good purpose. They were defined
early on to demonstrate that metaprogramming can give us Coq-like
notation, but really, we have much more interesting demos.
* Added single step meta-function to core
* Expose step/syn in redex-lang
* Added macro to sugar for convenience use
* Updated relevant docs (also fixed bug in reflection docs)
Yesterday's changes to sugar broke some things:
* case isn't smart enough to infer the right things in all cases yet, so
added previously existing case* for when it is necessary.
* reexport define-theorem and qed from sugar, since still used in prop.
* run is user-definable through the existing reflection features; moved
to sugar.
* define need not have special function support in curnel; moved to
sugar.
* fixed relevant documentation
