Add some commentary to KSBuffer
Add copy and assignment operators to the KSBuffer class
Add a test case for cloning a buffer.
Document KSBufferPrivate
Document KSBufferCL
Have KSBuffer ctor instead of KSContext factory method

Internally, the object is still constructed through the
KSContext, but this gives us the flexibility to allocate the KSBuffer
object on the heap or on the stack, as we choose.