Examples and generated code of each feature of pin-project

Basic usage of #[pin_project] on structs

• example
• generated code

Basic usage of #[pin_project] on enums

• example
• generated code

Manual implementation of Unpin by UnsafeUnpin

• example
• generated code
• UnsafeUnpin documentation

Manual implementation of Drop by #[pinned_drop]

• example
• generated code
• #[pinned_drop] documentation

project_replace() method

• example
• generated code
• project_replace() documentation

Ensure !Unpin by #[pin_project(!Unpin)]

• example
• generated code
• !Unpin documentation