Show hex dump of memory.

: .0 ( u1 u2 -- )
Display the contents of u1 right-aligned in a field u2 characters wide, 
preceded by zeroes. If the number of characters required to display u1 is 
greater than u2, all digits are displayed with no leading zeroes, in a 
field as wide as necessary.

: >prt ( c1 -- c2 )
If c1 if a printable char, then c2=c1. Otherwise, c2 is the code of the 
dot character ('.'). 

: ptype ( addr u -- )
Show a string. All unprintable chars are changed to dots.

: dump ( addr u -- ) \ ANS94 tools
Show hex dump.
