Clean up clippy lints in lib.rs
//! method.
//!
//! ```ignore
-//! fn main() {
//! let mut peripherals = stm32f30x::Peripherals::take().unwrap();
//! peripherals.GPIOA.odr.write(|w| w.bits(1));
-//! }
//! ```
//!
//! This method can only be successfully called *once* -- that's why the method returns an `Option`.
//! Subsequent calls to the method will result in a `None` value being returned.
//!
//! ```ignore
-//! fn main() {
//! let ok = stm32f30x::Peripherals::take().unwrap();
//! let panics = stm32f30x::Peripherals::take().unwrap();
-//! }
//! ```
//!
//! The singleton property can be *unsafely* bypassed using the `ptr` static method which is
