This introduces an internal glLoader library which allows
most of the implementation to be agnostic about the
implementation of the GL loading library. Specifically,
this removes references to the GLEW headers and libraries
from the rest of the source code and build system.
- changed the main OPENSUBDIV_INCLUDE_DIR to exclude ./opensubdiv
- updated CMakeLists.txt files in non-examples to use only this path
- updated CMakeLists.txt files in examples to append ./opensubdiv to path
- updated source in regression/common to use #include <opensubdiv/...>
- updated source in examples/common to use #include <opensubdiv/...>
- deferred source in examples to be updated on a case-by-case basis
- the framebuffer class in examples/common is unstable in certain drivers.
removing offscreen rendering for now.
- move screenshot function to GLUtils.
- fix vertex attrib binding bug (not showing control mesh on osx)
- add GLControlMeshDisplay and D3D11ControlMeshDisplay into
examples/common
- delete all drawCageEdges/drawCageVertices from viewers and
use ControlMeshDisplay class
