v0.18.0

• cocoa and core-graphics updates.
• Breaking: Added OsError variant to ContextError.
• Improved glX error reporting.
• The iOS backend no longer fails to compile... again (added iOS testing on CI to prevent further issues).
• Update winit dependency to 0.17.0. See winit's CHANGELOG for more info.

v0.17.0

• Fix regression that prevented automatic graphics switching in MacOS (#980)
• Add ContextBuilder::with_double_buffer function
• Add ContextBuilder::with_hardware_acceleration function
• Work around a presumed Android emulator bug
  that would cause context creation to return CreationError::OpenGlVersionNotSupported
  in some configurations
  (#1036)
• Update winit dependency to 0.16.0. See winit's CHANGELOG for more info.
• The iOS backend no longer fails to compile.