`Weekday` and `Time` (and probably more types) do not respect formatting flags

[jrpear]

println!("{:>10}", time::Weekday::Monday);

Gives

Monday

It should give

    Monday

This is because time's Display implementations don't look at the formatting flags on the Formatter passed.

fmt::Formatter::pad can do this automatically.

[jhpratt]

This can definitely be done. A quick look shows that Weekday will be trivial. Time will be slightly more involved, as I'll have to calculate the width up-front. The same is true for other types, I imagine.

[jhpratt]

Done on main.