Make LuaStack::Load return special codes for 'slash command', 'white space', and 'truncated lua'

luprex/cpp/core/util.hpp

@@ -110,6 +110,9 @@ bool is_lua_classname(string_view s);
 // Return true if the line of code is a lua comment.
 bool is_lua_comment(string_view s);
 
+// Return true if the line is entirely whitespace.
+bool is_whitespace(string_view s);
+
 // Return the first character, but if the view is empty,
 // return zero.
 inline char zfront(string_view &s) {