109.52.00

- Exposed an extensible form of `make_command` so that
  inline-benchmarking and the other tools can add more commandline
  flags.
- A significant rewrite of `Core_bench`.

  The rewrite provides largely the same functionality as the older
  version.  The most visible external change is that the API makes it
  clear that `Core_bench` performs linear regressions to come up with
  its numbers.  Further, it allows running user-specified multivariate
  regressions in addition to the built in ones.

  The underlying code has been cleaned up in many ways, some of which
  are aimed at improving the implementation of inline benchmarking
  (the `BENCH` syntax, which has not yet been released).