Lesson improvements

[rhornung67]

• Add example(s) of basic pointer introspection, or maybe this add to the example where data is allocated on the CPU and GPU and copied between them.
• Show use of allocator id integral values in addition to string name identifiers. Also, add some text in the lessons about why this may be preferred.
• Printing of results of reductions in codes for lessons 5-8. So users can check their work.
• Add result verification function to codes for lessons 9-10 (matrix multiplication) similar to what's in RAJA tutorial exercises.
• Fill in text in README for lesson 11.