Add assign() to Program.
0.5.44
Set _last in flag().
0.5.45
Define toObject() on Argument.
0.5.46
Expose class constructor.
0.5.47
Update constructor.
0.5.48
Use named constructors.
0.5.49
Expose toObject() on Command.
0.5.50
Use named constructor (Command).
0.5.51
Update toObject().
0.5.52
Allow write in options() and commands().
0.5.53