message: explicitly forbid having both client features enabled
diff: //! ](https://github.com/ramsayleung/rspotify/tree/master/examples)
  //! which can serve as a learning tool.
  +// disable all modules when both client features are enabled, this way only the compile error below gets
  +// show instead of showing a whole list of confusing errors
  +#[cfg(not(all(feature = "client-reqwest", feature = "client-ureq")))]
  pub mod client;
  +#[cfg(not(all(feature = "client-reqwest", feature = "client-ureq")))]
  mod http;
  +#[cfg(not(all(feature = "client-reqwest", feature = "client-ureq")))]
  pub mod model;
  +#[cfg(not(all(feature = "client-reqwest", feature = "client-ureq")))]
  pub mod oauth2;
  +#[cfg(not(all(feature = "client-reqwest", feature = "client-ureq")))]
  pub mod util;
  +#[cfg(all(feature = "client-reqwest", feature = "client-ureq"))]
  +compile_error!("`client-reqwest` and `client-ureq` features cannot be both enabled at the same time, if you want to use `client-ureq` you need to set `default-features = false`");
  +
  #[doc(hidden)]
  mod macros {
  /// Reduce boilerplate when inserting new elements in a JSON object.
  