Add Lucky::Params#[] methods

[grepsedawk]

It's always a bit of a shock to try params["param_name"] and get method undefined

Similar to #1678, I would love it if we added [] methods to params

[jwoertink]

We can't really do this without forcing all Avram::Paramable objects to start acting like a hash. It would start throwing things off with all of the nested values because then we'd have to also support things like params["user"]["username"], or params["posts"][0]["title"].

What I do is just keep in mind that it's not a hash-like object. Maybe we just add a compile-time error when you try to use [] that says to use get, or links to docs or something?

[watzon]

The more things we can warn about at compile time the better in my opinion

[grepsedawk]

[] is just VERY much more pretty, and saves 5 characters in line length.
Even if it was just available at the root level params I still feel adding [] provides a ton of value here.

At the end of the day, [] doesn't mean "hash like", it's crystal's way of accepting keys and returning values, which is precisely what params does.

[grepsedawk]

[] is also intuitive and expected