* 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
Moved all curnel code into curnel/, and split the two kernel modules
into separate files. Now the trusted core and the module/#lang stuff are
in separate files. The #lang is now reprovided by "cur.rkt", which
should also provide core agnostic sugar.