Added new benchmark file; added benchmarked version of recursive slip interpreter
Added run-benchmarks file
Made an explicit difference between the two recursive slip interpreters

'rec slip meta-interpreter normal' should be evaluated by Racket.
'rec slip meta-interpreter traced' should be interpreted by the meta-tracing interpreter
Wrapped the tracing interpreter inside a module so some functions could be exported
Exported some more functions that are used in the trace
Updated with new paths for recursive slip interpreters