Benchmark: adds Namespace.{hash,to_filename,Map}
This MR adds Namespace.hash, Namespace.Map, and Namespace.to_filename.
The first 2 are trivial.
Namespace.to_filename converts a namespace to a string appropriate for a filename, i.e. "foo__bar__boo.txt" for foo/bar/boo.txt . The function is required to save the benchmark results by their names.