Add context switch callback (closes #28)
Use move to save std::functions
Merge branch 'master' into manual_context_switch_callbacks

Conflicts:
	codegeneration/scripts/templates/Binding.h.in
	source/glbinding/include/glbinding/Binding.h
	source/glbinding/source/Binding.cpp
Merge branch 'master' into manual_context_switch_callbacks
Update README.md
Merge pull request #55 from hpicgs/manual_context_switch_callbacks

Add context switch callback (closes #28)