v0.4.2

[notgull]

• Add the ability to get the underlying window handle. (Add ability to get underlying window handle #193)
• Rework the backend to use a trait-based interface. (Use traits to define common backend interface #196)
• On Orbital, fix window resize. (On Orbital, fix window resize. #200)
• Fix bytes() for KMS/DRM implementation. (Implement BufferInterface::pixels for KMS backend #203)