Remove mention of std feature from docs

Author: JSorngard

README.md

@@ -112,9 +112,7 @@ assert_eq!(TOO_BIG, None);
 
 and more!
 
-## Feature flags
-
-`std`: implements the `Error` trait from the standard library for the error types.
+## Features
 
 `serde`: derives the `Serialize` and `Deserialize` traits from [`serde`](https://crates.io/crates/serde)
 for the `Primes` struct, as well as a few others.

src/lib.rs

@@ -91,9 +91,7 @@
 //! ```
 //! and more!
 //!
-//! # Feature flags
-//!
-//! `std`: implements the [`Error`](std::error::Error) trait from the standard library for the error types.
+//! # Features
 //!
 //! `serde`: derives the [`Serialize`](serde::Serialize) and [`Deserialize`](serde::Deserialize) traits from [`serde`](https://docs.rs/serde/latest/serde/) for the [`Primes`] struct, as well as a few others.