Implement switch fields bonus
Don't use the draw mutex anymore
Improve drawing area layout
Send the new field to both player in switch field
Fix bonus drop
Avoid infinite loop when computing shadow
blblbl
Add kept piece to libtetris
Add bindings for kept piece
Support kept piece in the server and add it to the protocol
Document kept.keep
Basic support of kept pieces in the client
Bind c to keep a piece
Correctly initialize kept piece
Fix kept piece