Develop a program to encrypt (encode) input data using the PlayFair
Digram code - which is so topsecret that you will be given a stub for testing.
This code takes each pair of input characters and encodes them into two
output characters.

The output (as in all cypher texts) will be output with 5 characters per
group and 10 groups per line (except possibly the last group on the last
line).

The input will be a sequence of letters and digits.  No input checking
is required.

The input data is from the standard input and the output is sent to
standard output - so that the program can be used as a filter as part of a
pipeline of other data handling processes.

No form of interaction with the user or other data than standard input
and output is required or desirable.

A good solution will be simple. A prototype needs to be ready as soon as 
possible.