add cotire 1.6.5 to speed up builds
enable testing through cmake
update stb_image to 1.4.6
fix stb image int ptr cast warning
remove glfw docs
add raii bind unbind for opengl primitives
add imgui (v1.10) support
add custom assert macro
add move semantics to bunch of classes
remove include guards, change to pragma once
add task manager, change slot map to templates

Pull out ID union to be templated class, use as ID<Entity> or ID<Task>. These
ids are then used by slot map which has been templated.
change test lib to catch v1.0b53 from gtest