Support for features / optional dependencies

[repo-helper]

Support for features / optional dependencies

[maresb]

@ofek, I attempted an implementation in #13. However I don't understand why you suggest above calling the replacement optional-dependencies section features. According to my tastes, it introduces redundant and confusing terminology, but on the other hand, you tend to have good reasons for your design decisions. 😄 Which name shall we use?

[ofek]

oh awesome! it's up to you, Hatch refers to them as features b/c it's easier to type/remember and it matches https://doc.rust-lang.org/cargo/reference/features.html

[maresb]

Great, thanks for the context! I'd prefer to keep optional-dependencies, but I added that groups of optional dependencies are "also known as "features"" in the README.