Added section base and length symbols to lwlink Added the ability for a link script to define section base and section length symbols when linking. These symbols are searched for when an external reference is resolved before looking up any symbols in the various objects being linked. Also documented the new link script directives and added such directives to all default link scripts.

The lwbasic directory is an in-progress attempt to write a compiler for a
dialect of basic specifically targetted at the 6809 CPU. It is still
incomplete but is included in this distribution in case someone finds the
code useful. It is not built by default.