autotuner-v1 release

The autotuner-v1 release contains the code used to generate the results of
the following paper:

J. Jung, A. B. Kahng, S. Kim and R. Varadarajan, “METRICS2.1 and Flow
Tuning in the IEEE CEDA Robust Design Flow and OpenROAD", Proc. ACM/IEEE
International Conference on Computer-Aided Design, 2021, pp. 1-9. (Invited
Paper)