Multiple renderbuffer-related changes

- Added overloads of Storage() that use images::ImageSpec to Renderbuffer
  and DSARenderbufferEXT.
- Added syntax sugar operators.
Multiple framebuffer-related changes.

- Added the syntax-sugar operators.
- Updated several examples to show the new features.
Multiple buffer-related changes

- Added the syntax-sugar operators to Buffer and DSABufferEXT.
- Updated examples to show the new features.
- Other minor changes.