Adding Debug derives

[vmx]

As there will be a new release soon, I thought it's the right to bring up another thing.

It would be great if there could be Debug implementations for the types. I guess for most of them a #[derive(Debug)] is good enough. It's useful e.g. if you've several buffers and want to distinguish them during debugging. Though I'd actually need it for my code base for ExecuteKernel and CommandQueue.

As always I'd be happy to provide a pull request if that helps.

[kenba]

Another good one @vmx. I've added #[derive(Debug)] to all the types that didn't have Debug implementations including ExecuteKernel and CommandQueue. The changes are in the develop branch.

Please provide a pull request if the changes do not meet your needs and feel free to raise any other issues you have with the library.

[vmx]

I haven't had a closer look at your changes, but for my use case I was able to derive the Debug from the types that I've used. Thanks!