Faster digest

[vinniefalco]

When calculating digests of strings, we could operate 4 or 8 characters at a time. First we need to run the profile to see what the current digest algorithm costs us during parsing.

[grisumbras]

Here's my benchmarking based on 4 approaches from PR #606 (each commit is a different approach).
https://disk.yandex.ru/i/7tKxDT2YG3o-Yw