/// Enables immutable call chaining on all types.
///
/// # Example
///
/// ```rust
/// use chainer::*;
///
/// struct HelloWorld;
/// impl HelloWorld {
/// fn print(&self) {
/// println!("Hello, world!");
/// }
/// }
///
/// fn main() {
/// HelloWorld
/// .chain(HelloWorld::print)
/// .chain(HelloWorld::print)
/// .chain(HelloWorld::print);
///
/// // Hello, world!
/// // Hello, world!
/// // Hello, world!
/// }
/// ```
/// Enables mutable call chaining on all types.
///
/// # Example
///
/// ```rust
/// use chainer::*;
///
/// struct Counter { value: i32 }
/// impl Counter {
/// fn increment(&mut self) {
/// self.value += 1;
/// println!("{}", self.value);
/// }
/// }
///
/// fn main() {
/// Counter { value: 0 }
/// .chain_mut(Counter::increment)
/// .chain_mut(Counter::increment)
/// .chain_mut(Counter::increment);
///
/// // 1
/// // 2
/// // 3
/// }
/// ```