message: Enable more aggressive compiler and clippy lints
diff: //!
  //! [https://nats.io/]: https://nats.io/
  //!
  +#![cfg_attr(test, deny(warnings))]
  +#![deny(
  + missing_docs,
  + future_incompatible,
  + nonstandard_style,
  + rust_2018_idioms,
  + missing_copy_implementations,
  + trivial_casts,
  + trivial_numeric_casts,
  + unsafe_code,
  + unused_qualifications
  +)]
  +#![deny(
  + // over time, consider enabling the following commented-out lints:
  + // clippy::else_if_without_else,
  + // clippy::indexing_slicing,
  + clippy::cast_lossless,
  + clippy::cast_possible_truncation,
  + clippy::cast_possible_wrap,
  + clippy::cast_precision_loss,
  + clippy::cast_sign_loss,
  + clippy::checked_conversions,
  + clippy::decimal_literal_representation,
  + clippy::doc_markdown,
  + clippy::empty_enum,
  + clippy::explicit_into_iter_loop,
  + clippy::explicit_iter_loop,
  + clippy::expl_impl_clone_on_copy,
  + clippy::fallible_impl_from,
  + clippy::filter_map,
  + clippy::filter_map_next,
  + clippy::find_map,
  + clippy::float_arithmetic,
  + clippy::get_unwrap,
  + clippy::if_not_else,
  + clippy::inline_always,
  + clippy::invalid_upcast_comparisons,
  + clippy::items_after_statements,
  + clippy::map_flatten,
  + clippy::match_same_arms,
  + clippy::maybe_infinite_iter,
  + clippy::mem_forget,
  + clippy::missing_const_for_fn,
  + clippy::module_name_repetitions,
  + clippy::multiple_crate_versions,
  + clippy::multiple_inherent_impl,
  + clippy::mut_mut,
  + clippy::needless_borrow,
  + clippy::needless_continue,
  + clippy::needless_pass_by_value,
  + clippy::non_ascii_literal,
  + clippy::option_map_unwrap_or,
  + clippy::option_map_unwrap_or_else,
  + clippy::path_buf_push_overwrite,
  + clippy::print_stdout,
  + clippy::pub_enum_variant_names,
  + clippy::redundant_closure_for_method_calls,
  + clippy::replace_consts,
  + clippy::result_map_unwrap_or_else,
  + clippy::shadow_reuse,
  + clippy::shadow_same,
  + clippy::shadow_unrelated,
  + clippy::single_match_else,
  + clippy::string_add,
  + clippy::string_add_assign,
  + clippy::type_repetition_in_bounds,
  + clippy::unicode_not_nfc,
  + clippy::unimplemented,
  + clippy::unseparated_literal_suffix,
  + clippy::used_underscore_binding,
  + clippy::wildcard_dependencies,
  + clippy::wildcard_enum_match_arm,
  + clippy::wrong_pub_self_convention,
  +)]
  +
  use std::collections::{HashMap, VecDeque};
  use std::io::{self, BufReader, BufWriter, Error, ErrorKind, Write};
  use std::net::{Shutdown, SocketAddr, TcpStream};
  