make sure that stack_aligned_stack_handler_function behaves properly

examples/source/stack_aligned_stack_handler_function.cpp

@@ -0,0 +1,45 @@
+#define SOL_CHECK_ARGUMENTS 1
+#include <sol/sol.hpp>
+
+#include "assert.hpp"
+
+int main(int, char* []) {
+	sol::state lua;
+	lua.script("function func (a, b) return (a + b) * 2 end");
+
+	sol::reference func_ref = lua["func"];
+
+	// maybe this is in a lua_CFunction you bind,
+	// or maybe you're trying to work with a pre-existing system
+	// maybe you've used a custom lua_load call, or you're working
+	// with state_view's load(lua_Reader, ...) call...
+	// here's a little bit of how you can work with the stack
+	lua_State* L = lua.lua_state();
+
+	// this is a handler:
+	// stack_aligned_stack_handler,
+	// as its type name explains so verbosely,
+	// expects the handler on the stack
+	sol::stack_reference traceback_handler(L, -sol::stack::push(L, sol::default_traceback_error_handler));
+	// then, you need the function
+	// to be on the stack
+	func_ref.push();
+	sol::stack_aligned_stack_handler_function func(L, -1, traceback_handler);
+	lua_pushinteger(L, 5); // argument 1, using plain API
+	lua_pushinteger(L, 6); // argument 2
+
+	// take 2 arguments from the top,
+	// and use "stack_aligned_function" to call
+	int result = func(sol::stack_count(2));
+	// function call pops function and arguments,
+	// leaves result on the stack for us
+	// but we must manually clean the traceback handler
+	// manually pop traceback handler
+	traceback_handler.pop();
+
+	// make sure everything is clean
+	c_assert(result == 22);
+	c_assert(lua.stack_top() == 0); // stack is empty/balanced
+
+	return 0;
+}