Added main code file.
Added text file containing keywords.

This file can be added to the PB IDE directly.
Added basic compiler constants.
Added string macros.
Added macro to check whether a constant has been defined.
Added 'true', 'false' and 'null' macros.
Added option macros (option explicit, option debugger).
Added type cast macros (via option extensions).
Added module macros (using / include).
Added 'boolean' macro for shorthand casting.
Implemented assert macro for both console and GUI.
Added build script (batch file).
Added more constants providing further information about the system.
Added structures for simplified array access.
Updated readme.md.
Added pb.mod logo.
Added title image to readme.md.