v0.2.0

Added

• std::containers::HashSet now implements Validate along with the other stdlib containers.
• Added option_min and option_max field attribute validators.

Changed

• Breaking Change Using a literal string in macro annotations will now be interpreted as an
  expression. This makes it possible to inject values by running functions and using types such as
  Some(42) with comparison operators. To inject string literals into macro attributes you will now
  now need to escape the literal quotes like so: #[validatron(equal = "\"Foo\"")]