Prepare for v4.0.0 release

[lopopolo]

Release rand_mt 4.0.0. This release is a new major version and contains breaking changes.

rand_mt is published on crates.io.

This release contains enhancements and breaking changes:

• [BREAKING] rand_mt requires at least Rust 1.47.0. Derive Hash, PartialEq, Eq, PartialOrd, Ord on mersenne twister RNGs #49
• [BREAKING] Update rand_core dependency to 0.6.0. Update rand_core requirement from 0.5 to 0.6 #46
• [BREAKING] rand_core is an optional dependency. Activate implementations of rand_core::RngCore by enabling the rand-traits feature. Make the dependency on rand_core optional #50
• Implement the core Mt and Mt64 APIs as methods on the types' inherent impl block. Make the dependency on rand_core optional #50
• Derive Hash, PartialEq, Eq, PartialOrd, Ord using built-in derive macros. Derive Hash, PartialEq, Eq, PartialOrd, Ord on mersenne twister RNGs #49
• Update version-sync dev dependency to 0.9. Update version-sync to 0.9 #28
• Remove doc-comment dev dependency and replace with a small, inlined macro. Replace doc_comment dev-dependency with a small inlined macro_rules macro #35
• Remove quickcheck and quickcheck_macros dev dependencies; use getrandom instead. Remove quickcheck dev-dependency #53

This release contains improvements to documentation, testing, and release packaging.