Return codes and error messages

When the Type Tree Maker finds a problem with a command, it returns either an error message or a warning message, depending on the severity of the problem. These error and warning messages, viewable from the Type Tree Maker, are also stored in the install_dir/ttmaker.log file.

The ttmaker.log file record contains the line number of the command that caused the error or warning message, followed by a message. An example of a warning message is Warning 34 at line 3: Overwrote existing type (and possible subtree).