feat: Add a or! macro to make or chaining more readable

[Marwes]

There are some earlier discussions about more complicated macros (#26 and #395). But I believe a simple or! macro is quite useful on its own as it lets long .or chains be written without having the first filter being aligned differently or .or getting lost in the noise.

(Originally I called this choice! because of the equivalent macro I use in combine https://docs.rs/combine/4.0.1/combine/macro.choice.html but or! is probably more understandable. It could also be written as a function, using tuples to fake varargs https://docs.rs/combine/4.0.1/combine/fn.choice.html)