Add extClass convinience utiltiy for use-cases where CSS is provided externally

[kfigiela]

In response to the question in the other PR https://github.com/seanhess/web-view/pull/3#discussion_r1638420071 this helper makes it easier to add classes to HTML elements that are defined in 3rd party CSS. This is what I've been using in my project. Alternatively, IsString instance could be added to Class so addClass can be used directly. This however, can cause some confusion for people who will use web-view "as prescribed", as it'd be pretty easy to confuse addClass $ cls "foo" & prop "foo" "bar" with addClass "foo" & prop "foo" "bar"

[seanhess]

Great, thanks for this!

I feel like the name cls_ is confusing, because it's not really an alternative to the cls constructor, it's an alternative to addClass. What do you think about naming it something like addClass_ or addClassName? It helps communicate that it's not setting the entire class attribute, just adding a single class (it handles spaces for you, etc)

[kfigiela]

Yeah, naming is hard. Personally, I'd pick something short as this is going to be used a lot if user decides to use external CSS. How about externalClass or extClass so it's harder to confuse?

[seanhess]

Let's go with extClass since it'll be used frequently

[kfigiela]

Adjusted & force pushed