Reverting "Add flipping and modernize the codebase a bit"
Revert "Add flipping and modernize the codebase a bit"

This reverts commit c7a3de714baa5fbda46a15c7bb45d7b72da9046c.
Revert "Factor out the texture rendering and delete unnecessary layer types."

This reverts commit 72df15a794a11325ff075b4a3697848870e11c59.

Conflicts:
	texturegl.rs
Update for latest Rust.
Warning police.
Implement cross-process surfaces on both Mac and Linux.

Also add support for both GL_TEXTURE_2D and GL_TEXTURE_RECTANGLE_ARB. The
latter is needed for cross-process surface support on Mac.