v0.2.0 release!

What's new:

• Added new Command.takesValue setter (f6ca476)
• Added new Arg.takesMultipleValues API which allows Arg to take unknown number of values (f5e6512)

Internal changes:

• fix(Parser): Set ErrorContext.setErr(err) when error is captured on else (98aee00)
• refactor(Parser): Add a function to verify and append the value (c734d0c)
• fix(Parser): Use a pointer capture instead of value capture (7caff04)