Fixes related to make doc handling of script summary text (##! comments)

- Summary comments (##!) can now be placed at the beginning of
BiF files (but still outside C segments).  An issue was fixed where
these comments would mistakenly be transferred into the generated
.func_def file and cause a compile error. I completely removed writing
any opt_ws value into the .func_def file because it was currently not
writing anything besides whitespace.

- The generation of reST for the collecting of "groups" of policy
script documentation now happens at build time of `make doc` through the
use of a helper script rather than doing this at configure time so that
changes to summary text will always be reflected in the documentation.

src/builtin-func.y

@@ -319,8 +319,8 @@ definitions:	definitions definition opt_ws
 			fprintf(fp_netvar_h, "// %s\n\n", auto_gen_comment);
 			fprintf(fp_netvar_init, "// %s\n\n", auto_gen_comment);
 
+			fprintf(fp_bro_init, "%s", $1);
 			fprintf(fp_bro_init, "export {\n");
-			fprintf(fp_func_def, "%s", $1);
 			}
 	;