Merge pull request #2 from ddemidov/master

Cleaned up VexCL-related code
correct offset error in nodal_diff macro for kkrev
removed obsolete internal function copy_subvector in favor of direct use of slice
renamed files to chebyshev_cl, made device vector methods modify vectors in place, changed Cython class to ChebyshevCL
renamed files to chebyshev_cl, made device vector methods modify vectors in place, changed Cython class to ChebyshevCL
Fix the misleading comment