PTLib - Portable Tools Library

PTLib is a moderately large class library that has it's genesis many
years ago as PWLib (Portable Windows Library), a method to produce
applications to run on both Microsoft Windows and Unix systems. It
has also been ported to many other systems.
Since then the system has grown to include many classes that assist
in writing complete multi-platform applications. So it became a
Portable Tools Library and was renamed to PTLib.
