Remove constant UTF_16_NULL. The constant is now in constants.rb instead
Forgot to commit constants.rb last time
Implement DlgCmdEntry-class

Implement Subdialog-class
Implement DlgIdxFile-class
Implement DlgCmdFile-class
Implement dlgcmd tool. This tool is used to split/merge dlgcmd- and dlgidx-files. Run 'ruby dlgcmd_tool.rb -h' for help