Move *CodeFile and *Line classes to lang/ subdir

To provide a less cluttered and more organized repository, the numerous
but sparsely implemented *CodeFile and *Line classes were moved to a
src/lang/ subdirectory.  This at once identifies them as being alike
in nature, as well as separates them from unrelated files in the
project.

This commit also includes changes to the Makefile, and numerous
\#include statements found in files throughout the project, to reflect
the new location for each file.