Prior to this CL, --address-radix was being used to determine the format
of the output bytes. This was wrong: this flag controls the printing of
the address (in the POSIX spec for od, this is called the "input offset
base"), not the printing of the content bytes.
+ Make parse_radix terser and clearer.
+ Make purpose of radix clearer at use site
(note that the code currently completely misuses the --address-radix
flag; this is inherited from the previous code)
+ Don't panic! inside parse_radix; instead return Result<> and let the
caller handle errors (currently we panic, but probably we'll want to use
some less alarming error routine); this will be more testable later as
well.
