Fix TypeScript errors in Axis components

[rgieseke]

Here are fixes for the Axis components. I think they wouldn't be too overwhelming for non-Typescript users as discussed in #218

If you're fine with that level of additional typing I could try and see where else I could make similar changes (probably in bits whenever I have some time).

One thing I'm not sure about in this PR is the whether this is correct. Can the Array only contain numbers, or also potentially strings?

/** @type {Number|Array<Number>|Function|undefined} [ticks] - If this is a number, it passes that along to the [d3Scale.ticks](https://github.com/d3/d3-scale) function. If this is an array, hardcodes the ticks to those values. If it's a function, passes along the default tick values and expects an array of tick values in return. If nothing, it uses the default ticks supplied by the D3 function. */
export let ticks = undefined;

[mhkeller]

These look great. I had thought we'd have to do more inline type definitions such as function thing (d /* type stuff here*/) { } which would visually throw some folks off.

[rgieseke]

These look great. I had thought we'd have to do more inline type definitions such as function thing (d /* type stuff here*/) { } which would visually throw some folks off.

Yes, fully agreeing!

I need to give this more thought, I think the different ticks, tickVals and format function types need to be properly aligned.