Release 0.8.0

Breaking Changes:

• Style::new() and Style::create() now takes a new trait IntoSheet for
  Stylesheet which is implemented by default for both
  stylist::ast::Sheet and everything that implements AsRef<str>.
• Feature yew has been renamed back to yew_integration.
• Selectors list now gets a class name added for each selector.
• Style is now !Send and !Sync.
• Stylist now treats pseudo class selectors (e.g.::hover) like emotion
  and styled-components.

Other Changes:

• Added a GlobalStyle struct to register global styles.
• Added a <Global /> Component for global styling for yew applications.
• Supported @supports CSS at-rule.
• Added an alternative counter-based class name on the style when
  feature random is disabled.
• Added a StyleManager type to manage the behaviour of styles.
• Moved AST and Parser logic to a new crate stylist_core.
• AST has been exposed under stylist::ast.
• Improved performance for looking up cached styles.
• Improved Examples.
• Documentation now shows feature flags.