Some people want a function

   char *Elk_Eval(char *expr);

that receives as an argument a string containing a Scheme expression
and returns the result of evaluating the string or a null pointer if
an error occurred.

Elk_Eval() stores its result in a static buffer of fixed size; this
can be improved easily by passing a buffer and a length as additional
arguments.

You can test Elk_Eval() by compiling elk-eval.c (with a -I option
pointing to Elk's include directory, and CFLAGS as specified in your
site's config file), then compiling test.o, and loading elk-eval.o and
then test.o into Elk.
