Remove zerocopy from rand (#1579)

Replace `zerocopy` dependency with `unsafe` code.
Add benchmarks for some SIMD / wide types.
Document all `unsafe` code.

Author: dhardy

src/lib.rs

@@ -31,6 +31,7 @@
 )]
 #![deny(missing_docs)]
 #![deny(missing_debug_implementations)]
+#![deny(clippy::undocumented_unsafe_blocks)]
 #![doc(test(attr(allow(unused_variables), deny(warnings))))]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 #![no_std]