bump to v2.0.21

[enricozb]

No description provided.

[HigherOrderBot]

Perf run for 95237ae:

compiled
========

file            runtime         main            (local)       
==============================================================
sort_bitonic    c                       10.09s          11.03s
                cuda                     0.14s           0.14s
--------------------------------------------------------------
sum_rec         c                        2.37s           2.41s
                cuda                     0.05s           0.05s
--------------------------------------------------------------
sum_tree        c                        0.29s           0.23s
                cuda                     0.02s           0.02s
--------------------------------------------------------------
tuples          c                        8.79s          10.94s
                cuda                   timeout         timeout
--------------------------------------------------------------

interpreted
===========

file            runtime         main            (local)       
==============================================================
sort_bitonic    c                       10.05s         timeout
                cuda                     0.14s           0.14s
                rust                   timeout         timeout
--------------------------------------------------------------
sum_rec         c                        5.40s           7.59s
                cuda                     0.05s           0.05s
                rust                   timeout         timeout
--------------------------------------------------------------
sum_tree        c                        0.70s           0.41s
                cuda                     0.01s           0.01s
                rust                     2.09s           1.96s
--------------------------------------------------------------
tuples          c                        7.29s           7.61s
                cuda                   timeout         timeout
                rust                     8.76s           8.91s
--------------------------------------------------------------