Proc macro development utilities

Features

Feature	Description
default	["derive"]
attr_parse	Attribute parsing utilities, attr_parse.
derive	Enable derive macros. Currently requires the attr_parse feature to do anything.
full	Enable syn/full. If attr_parse is enabled, it'll implement the traits for types that require syn/full.
nightly	Enable some nightly Rust optimisations during macro execution only, has no effect on generated code.