Use mandala testlib.TestImage
Pass a shader program to the shape constructor instead of instantiating a program for each shape created
Merge branch 'fix_shader_link_error'

Conflicts:
	box.go
	test/src/testlib/tests.go
Use imagetest.Center as adjuster in testlib.TestImage
Merge branch 'master' of https://github.com/remogatto/shapes
Added partial texture test
Starting the refactoring