dpp: add a syntax for parsing strings

@"foo" will expand to ecl_make_constant_base_string("foo", -1) now.
That saves some typing during testing when we want to feed a string to
the cl_format and other CL functions opearting on strings.

Now:

cl_format(3, @"~a: ~s", obj1, obj2);

Then:

cl_object str = ecl_make_constant_base_string("~a: ~s", -1);
cl_format(3, str, obj1, obj2);

src/c/dpp.c

@@ -351,6 +351,20 @@ read_symbol(int code)
   return name;
 }
 
+char *
+read_string()
+{
+  char c, *str = poolp;
+  char end = '"';
+  pushstr("ecl_make_constant_base_string(\"");
+  do {
+    c = readc();
+    pushc(c);
+  } while (c != end);
+  pushstr(", -1)\0");
+  return str;
+}
+
 char *
 search_function(char *name)
 {
@@ -441,6 +455,9 @@ read_token(void)
         poolp--;
       } else if (c == '@') {
         pushc(c);
+      } else if (c == '"') {
+        read_string();
+        poolp--;
       } else {
         char *name;
         unreadc(c);
@@ -933,6 +950,13 @@ main_loop(void)
     fprintf(out,"%s",p);
     poolp = tmp;
     goto LOOP;
+  } else if (c == '"') {
+    char *p;
+    char * tmp = poolp;
+    p = read_string();
+    fprintf(out,"%s",p);
+    poolp = tmp;
+    goto LOOP;
   } else if (c != '(') {
     char *p;
     char * tmp = poolp;