Changed ticks function from &mut self to &self.

[aneilmac]

Hi there,

Currently, the ticks method requires a &mut self, which this PR downgrades to a &self.

Please let me know if I've made a mistake in my understanding here. I think &self should be fairly benign; AFAIK ticks doesn't do anything mutable under the hood.

What motivated this change is I can't check the elapsed ticks while I have a living Timer object due to the borrow checker. If I have missed a good reason this function is marked as mutable then please let me know.

[Cobrand]

I think you're safe with changing that to a &self. You are probably the only one to use this though, since std::time::Duration exists and is much more widely used in Rust. Still, thanks!