argparse 0.5.0

• Actions can now be used to implement custom processing logic.
• Added actions for arguments.
• Added string aliases for actions such as store_false.
• Command actions are now called after the parsing, with result target as the argument.
• Added command_target property for storing name of used command.
• Improved error messages on missing arguments.
• -f123 is now interpreted as -f 123 when -f takes an optional argument.