Set Node.js v16 as minimum

[ngbrown]

Blocks #68 and #71

This bumps the minimum version of Node.js to v16. This is a breaking change and requires a major version increment.

• See supported Node.js release schedule at https://nodejs.org/en/about/releases/
• Node.js 12 reached end-of-life 2022-04-30
• Node.js 14 reached end-of-life 2023-04-30

Node.js v20 was included in the test matrix

[dentarg]

Looks good to me, hopefully rest of the team agrees with this, will merge as soon as I have some indication about that :)