Methods to_usize() etc should be const-fn

[Boscop]

The methods [to_usize()](Methods to_usize() etc should be const-fn) etc should be const-fn.

[Boscop]

Nevermind, trait fns cannot be declared const :/

[PTaylor-us]

On nightly, one can impl const Trait for T. Perhaps something like that could be used.

I'm going to play around with it and see what the possibilities are.

[PTaylor-us]

I'm not having a huge amount of success. Here's where I'm at: playground