Update description
Add Gaku::Deck#stats returning deck statistics
Mend card moving

Cards are moved one step too far causing uncomfortable ordering. Let's
move them the correct distance instead.
Add Gaku::Options for parsing CLI options
Have Gaku:Config raise error if config invalid

Seems like a better idea to throw exception and quit early than to need
to use #valid? to know if things went well.
Show something nicer than a stack trace if config broken
Set proper error message when options not valid
Tidy Gaku::CLI a bit
wip: kanji.deck
wip: swahili animals
Add Gaku::Colouring, for coloured output
Use Gaku::Options for ARGV in CLI
Show stats given --stats
Save deck directly after wrong answer
Add Gaku::ProgressBar
wip: add progressbar to cli
wip: implement colouring in CLI
wip_toe
fixup (something) increase minimum card distance 1 => 2
wipwip