Fix ISO standard number
Merge pull request #110 from stephen-turner/ISO

Fix ISO standard number
Abstract from the specifics of the chess ELO calculations (part 1)
Move "stakes" calculation into the Chess module
Add game length to calculations, needed for backgammon
Add Stephen's backgammon rating algorithm
Customise ladder description
Add game length to JSON output
Optionally print game length in print command
Allow specifying the game type on the command line
Update man pages and readme