Examples for all features

[Nemo157]

Currently there's just the one basic example. The docs should be extended to show all the different features. There should be tests covering them all so basically need to take a good subset of the tests, clean them up, add some notes, and put them in the crate docs.

Quick list of what features I can think of right now:

• attire(scope) - setting a wrapper attribute
• attire(default) - setting a default if unspecified
• FromStr parsing - parsing strings passed in as values
• attire(docs) - putting docs attributes into a place
• attire(attribute) - setting a different attribute name to use (⚠️🚴🏠 Maybe rename #[attire(attribute=)] #9)
• attire(split_attribute_of) - complicated, semi-unstable (Reconsider #[attire(split_attribute_of=)] #10)
• attire(flag_value) - set a default if the attribute is used without a value, (⚠️🚴🏠 Maybe rename #[attire(flag_value=)] #11)
• literals - support for non-string literals (currently unstable in Rust, but supported by syn)
• bool - special cased default and flag_value
• Vec - attributes that can take multiple values
• errors - the errors that can be returned during parsing
• lifetimes - borrowing strings from the AST