Primitives for transaction weighting.

Latest machine specification used to benchmark are:

• Digital Ocean: ubuntu-s-2vcpu-4gb-ams3-01
• 2x Intel(R) Xeon(R) CPU E5-2650 v4 @ 2.20GHz
• 4GB RAM
• Ubuntu 19.10 (GNU/Linux 5.3.0-18-generic x86_64)
• rustc 1.42.0 (b8cedc004 2020-03-09)