Maintenance release

fix: #590 add Kernel.onActivate

- which is called after gpu.js switches kernels based off need
fix: Consistent error message for values that are not defined
fix: Add recompiled kernels to gpu.js kernels property and test
fix: Move texture deleting to within the GLKernel Texture implementation
fix: Add Texture.clear as an abstract method on the base Texture
fix: Bump and build