Add gloo-console-timer

[cbrevik]

Resolves #16

Adds the gloo-console-timer crate with the ConsoleTimer RAII type.

Docs feature the preferred scope-method for measurement:

let value = ConsoleTimer::scope("foo", || {
    // Place code to be measured here
});

Was a bit unsure how to write tests here, since it seems I cannot verify through tests that the measurement including label is printed to the console.

[fitzgen]

Looking good! Happy to merge with nitpicks below addressed.

Yeah hard to test since the effects aren't visible to us. I think what you have written is fine.

Thanks @cbrevik!

[cbrevik]

Addressed feedback, but I see one of the doc tests doesn't build, so will have to fix that first. (The one using gloo_timers).

[cbrevik]

Maybe there is a better way to handle this than to ignore the test?

I didn't want to add dependencies just to make that example compile.

[fitzgen]

Thanks @cbrevik!