Create a HELP command that loads the usage string of a command.

The HELP command accesses and displays the usage string of a command from the command.  

Example:
```
] HELP COPY

USAGE: COPY <SOURCE>, <DEST>

] HELP TYPE

USAGE: TYPE <FILE (TXT, BIN)>  

] HELP HELP

USAGE: HELP <Command>  gets the usage message from any CMD file and displays it.
```