Unify and correct error messages
Just a simple cleanup here. I'll leave it open for a couple days before merging in case anyone has comments.
OpenCL error messages are now prefixed correctly with coot::opencl::<function>():
for operations, and runtime initialization errors come with coot::cl_rt::init():
. CUDA error messages are coot::cuda::<function>():
and coot::cuda_rt::init():
. The idea here is to give the user a basic idea of what component might be having a problem, and to clearly identify it as a Bandicoot problem (which may not be immediately clear to users who are using code for which Bandicoot is a dependency that they may not be working directly with).