Playfair cipher

Implement a Playfair cipher encryption and decryption.

Playfair cipher is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

The user must be able to choose J = I or no Q in the alphabet. The output of the encrypted message must be in capitalized digraphs, separated by spaces.

Output example: HI DE TH EG OL DI NT HE TR EX ES TU MP.