Created a separate directory for low-level functions.
Moved error codes to Low subdirectory.
Moved tables of error and resource codes to Low subdirectory.
Moved high level function pages to High subdirectory.
Moved table of conditions and condition to High subdirectory.
Added table of contents specific to high-level interface.
Added table of contents specific to low-level interface.
Made table of contents refer to High and Low.
Fixed cut-and-paste error.
Moved file that ended up in the wrong subdirectory.
Removed low- prefix for referenced files.