*command
**
Form:           TAB "from/a,to/a,untab/s,full/s"
Purpose:        convert between spaces and tabs
Author:         PB
Specification:

   TAB will convert all (leading) spaces and tabs either into tabs followed by
any spaces that may be needed, or to all spaces. Unless full is specified, only
tabs and spaces at the start of a line are processed.
   It gives out a message to the initial output stream if there are more or less
characters in the output than the input

Examples:

                TAB filea fileb full            reduce the file size
                TAB fileb filea untab full      expand it back


