Complete API rewrite.

New dev tooling

• Node 18+ only
• yarn
• Typescript
• GH actions for CI
• ava for testing, with sinon for mocks, c8 and coveralls for coverage
• prettier

New API principles

• Zero dependencies (for users, of course we need devDependencies for development)
• Completely incompatible with fluent-ffmpeg 2.x. I'm still debating whether to include a compatibility layer that emits deprecation warnings, but that would be about the same work as rewriting 2.x from scratch.
• Natively typescript
• There is usually only one way to perform a given operation. No more methods with 42 aliases, or arguments that can be strings/arrays/objects and are a pain to validate.
• Replaced chaining with options object

await ffmpeg({
  input: 'path/to/input.webm',
  output: {
    target: 'path/to/output.mp4',
    video: { codec: 'h264', bitrate: '1M' },
    audio: false
  }
}).run()

Dropped features

The following features were not reimplemented:

• flvtool/flvmeta specifics; those should be mostly unused by now, people can still either use v2 or run flvtool/flvmeta themselves
• avconv/avprobe compatibility; libav is dead