style: s/non-terminal/nonterminal/

I personally prefer 'non terminal', or 'non-terminal', but
'nonterminal' is the common spelling.

* data/glr.c, src/parse-gram.y, src/symtab.c, src/symtab.h,
* tests/input.at, doc/refcard.tex: here.

data/glr.c

@@ -639,7 +639,7 @@ struct yyGLRState {
   size_t yyposn;
   union {
     /** First in a chain of alternative reductions producing the
-     *  non-terminal corresponding to this state, threaded through
+     *  nonterminal corresponding to this state, threaded through
      *  yynext.  */
     yySemanticOption* yyfirstVal;
     /** Semantic value for this state.  */