message: Give a hard error if outdated environment variables are set
  This avoids confusion where the environment variable works with some
  versions of docs.rs but fails silently with others.
diff: @@ -66,6 +66,26 @@ pub struct Config {
  impl Config {
  pub fn from_env() -> Result<Self, Error> {
  + let old_vars = [
  + ("CRATESFYI_PREFIX", "DOCSRS_PREFIX"),
  + ("CRATESFYI_DATABASE_URL", "DOCSRS_DATABASE_URL"),
  + ("CRATESFYI_GITHUB_ACCESSTOKEN", "DOCSRS_GITHUB_ACCESSTOKEN"),
  + ("CRATESFYI_RUSTWIDE_WORKSPACE", "DOCSRS_RUSTWIDE_WORKSPACE"),
  + ("CRATESFYI_TOOLCHAIN", "DOCSRS_TOOLCHAIN"),
  + ("DOCS_RS_DOCKER", "DOCSRS_DOCKER"),
  + ("DOCS_RS_LOCAL_DOCKER_IMAGE", "DOCSRS_DOCKER_IMAGE"),
  + ("DOCS_RS_BULID_CPU_LIMIT", "DOCSRS_BULID_CPU_LIMIT"),
  + ];
  + for (old_var, new_var) in old_vars {
  + if std::env::var(old_var).is_ok() {
  + failure::bail!(
  + "env variable {} is no longer accepted; use {} instead",
  + old_var,
  + new_var
  + );
  + }
  + }
  +
  let prefix: PathBuf = require_env("DOCSRS_PREFIX")?;
  Ok(Self {
  