Commands that need to modify the running user structure defined in scli.h 
should reside here. They (will) have a slightly different prototype that
allows passing the user structure to them for ease of modifications.

Examples of what should be a built-in and not a module would be:

cd     (the cwd needs to be updated)
prompt (the prompt needs to be updated)
enable (the euid needs to be updated)

.... etc.

Anything that does _not_ need to write to this structure should be included
as a module, not a built in.

For now, a skeleton directory of stuff that will exist lives here.