Use HEAD request to test whether endpoint exists

[dtolnay]

For example, check whether a particular GitHub user exists: https://api.github.com/users/ferris-the-crab

[gsquire]

I can do this one using the reqwest crate.

[dtolnay]

Great! Here is a method to make a HEAD request and GitHub should respond with 200 if the user exists and 404 if the user does not exist (or come up with your own better use case).