KernelBuilder is not cloneable

[michaelmattig]

The documentation says that it should be possible to clone a KernelBuilder like this: (https://docs.rs/ocl/0.19.3/ocl/builders/struct.KernelBuilder.html#examples)

// Clone the builder:
let mut builder_clone = builder.clone();

However, this code does not compile and

the trait std::clone::Clone is not implemented for ocl::builders::KernelBuilder<'_>

Also the release notes say that this functionality was added in version 0.19.1 https://github.com/cogciprocate/ocl/blob/master/RELEASES.md#version-0191-2018-09-28