Support for ExpressTools API

Since BricsCAD V14, we started implementing the API functions of AutoCAD "ExpressTools" as native functions, to improve compatibility for existing AutoLISP tools and applications, if they are based on this.optional Lisp interface.

The amount of those (acet-xxx) family functions is rather huge, so we started with the most-often used API functions, especially those functions originally implemented in "acetutil.arx", as these are more difficult to emulate with normal Lisp code (besides performance advantages by native implementation in C/C++ by Lisp engine).

This should not be confused with the end-users "ExpressTools for BricsCAD" functionality, which implements the majority of the (acet-xxx) API functions and end-user commands - this is  provided by www.cadwiesel.de and we are in cooperation to coordinate the ongoing work here.

These "ExpressTools" API functions are currently provided :