Start from scratch.

Scrap the old operator / indexing methods.

New approach:  Use the linear index parameterization idea from the 'linind'
branch, but:
 - instead of defining I/O methods that need to explicitly deal with input /
   output domains, define only the very core of the operation, and let the
   details be fleshed out by an operator generator.
 - let this operator generator handle generating code for whatever special cases
   may come up from the various use cases.
   E.g., optimizations for contiguous data, slower generalized version for
   arbitrary indexing.
Working on a stub for an operator generator.

Will encapsulate all the details of how to call the operator under different
circumstances.