Add IsLog type class

[jvliwanag]

JS console functions typically handle logging of certain types in a special manner. For instance, logging Errors also display an accompanying stack trace. Logging dom elements on browsers can also emits a dom tree that can be interactively inspected.

Pointing to purescript-debug might not always suffice, since there are use cases outside of debugging -- for instance logging errors with stack traces on server side purescript.

I've read that there used to be Any variants (logAny, warnAny) that were forall a. a -> Effect Unit, but have been removed.

Perhaps aa middleground between accepting anything vs limiting logging only to strings is to simply mark which types make sense to be logged. So I introduced the typeclass IsLog here and an instance for String and Array. I'm open to renaming this. (Logging extra long arrays auto truncates the array and offers interactive expanding on browsers)

Another option is to keep log only for strings, but introduce log' which accepts others that have an IsLog instance.

[hdgarrood]

The problem with this is that it's quite JS-specific, and for such a low-down library in the ecosystem I think we need to make sure that what we provide here makes sense in alternate backends, and I doubt this will. Plus, I don't think a type class is appropriate here, because pretty much any value can be displayed at least half-sensibly in a JS console if you just pass it to console.log. The only exceptions are types like Map which hide their representations. I think this approach would be a better fit for a separate library.