Add texthook option

`-texthook print` prints text to console, and `-texthook copy`
automatically copies text to clipboard (for use with text hooker tools).

On Windows, copy mode can be toggled from the menu bar.

src/sdlmain.cpp

@@ -97,6 +97,8 @@ int main(int argc, char *argv[])
 	EM_ASM( xsystem35.shell.windowSizeChanged(); );
 #endif
 
+	texthook_set_mode(config.texthook_mode);
+
 	int exit_code = NACT_RESTART;
 	while (exit_code == NACT_RESTART) {
 		exit_code = g_nact->mainloop();