Add special variables for keyword arguments & values.
Add support for keyword arguments to (simplify-apply).
Implement full string parsing in src/reader.rls.
TODO: Support keywords in (simplify-lambda) and writer.
Should simplify error-handling and sequences of primitive tests.
Also, automatically instantiate templates used in the tail-call lambda & cont'n fields.
This is to separate the three 'call' parameters (target, argv, ctx) from
the 'return to' parameter (k). The old order made it look as if the dynamic
context was in some way related to the continuation, which is not the case.
Jesse D. McDonald