Move MSRV to 1.42
//! needs matching memory layout to be efficient (with some exceptions).
//! + Efficient floating point matrix multiplication even for very large
//! matrices; can optionally use BLAS to improve it further.
-//! - **Requires Rust 1.40 or later**
+//! - **Requires Rust 1.42 or later**
//!
//! ## Crate Feature Flags
//!
