Support for classes inspection

[tim-hutchinson]

This PR has an implementation for #139 . I based the structure on the existing html and text methods that only work on a single instance, not an array.

Classes has a few tricky edge cases with CSS Modules. I don't use them in my own projects, so I don't have expertise on the right expected behavior, and couldn't find an official inverse function for them. With a CSS Module class that composes another class, both classes end up on the output. Right now, I'm returning both the extension and base classes back, but I don't know if this is the expected behavior. I'm also assuming that the base will always be defined in $style, but I haven't experience more exotic examples of CSS Modules (ie extending globals, etc).

[eddyerburgh]

Thanks @tim-hutchinson . I'd like to wait for some more feedback before we merge, but let's keep this open, and I'll merge once we've decided.

[eddyerburgh]

Would you be able to add attributes and props to this PR?

[tim-hutchinson]

Sure, I'll get them added.

I noticed before there are tests for WrapperArray in both test/unit/specs/mount/WrapperArray and test/unit/specs/wrappers/wrapper-array.spec.js. Do you prefer tests in both locations or just one?

[eddyerburgh]

Prefer tests in both locations

[tim-hutchinson]

One question on the spec for props. If there are no props, should it return undefined or {}? The component itself actually has it undefined, but an empty object/array is the behavior on the other inspection functions.

[eddyerburgh]

@tim-hutchinson can you fix the merge conflict?

[eddyerburgh]

Thanks @tim-hutchinson 😀

I'll add deprecation notices to hasClass, hasProp, and hasAttribute, and release later this week