Updates for Node 14 and ESM

[kristoferbaxter]

• ESM format source
• Autogenerate CJS main field source
• Use tap with parallelized tests
• Leverage volta for pinning node and yarn version
• Output export maps for node 14 and above
• Test node versions 6.x, 8.x, 10.x, 12.x, 14.x

NOTE This PR isn't meant to be consumed as is, but as a heads up of how some of this might work.

This PR is now ready for review, maintaining compatibility with older node versions but using ESM when available.

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Closes #31

[kristoferbaxter]

Bench results with Node 14.

# All Colors
  ansi-colors x 194,188 ops/sec ±0.33% (95 runs sampled)
  chalk x 635,888 ops/sec ±0.30% (95 runs sampled)
  kleur x 744,164 ops/sec ±0.50% (95 runs sampled)

# Stacked colors
  ansi-colors x 25,717 ops/sec ±0.38% (93 runs sampled)
  chalk x 604,484 ops/sec ±0.30% (97 runs sampled)
  kleur x 100,552 ops/sec ±0.25% (93 runs sampled)

# Nested colors
  ansi-colors x 77,884 ops/sec ±0.20% (94 runs sampled)
  chalk x 147,621 ops/sec ±0.61% (97 runs sampled)
  kleur x 155,266 ops/sec ±1.80% (94 runs sampled)

[lukeed]

Thank you for this. Hope you don't mind that I reduced some of the moving pieces. The ideas and the approaches are the same 👍

However, do you mind removing the test changes? I'm not opposed to the new tests (I'd have some suggestions for them), but they're not working in CI – and even if they were, it's too many large-scale moving chunks at once. I'd feel much better merging an exports PR that proves existing usage is preserved (eg, everything via require; to start...).

I'd much rather look at & discuss test changes separately.

Hope you understand!

[lukeed]

Also, the tests may be parallelized now, but they're significantly slower.

Node 6 tape: 24ms
Node 10 tape: 13ms
Node 14 tape: 12ms

Node 14 tap w/ require (new): 781ms
Node 14 tap w/ import (new): 702ms

[kristoferbaxter]

Happy to disentangle. Will be able to look at this in a few days.

[lukeed]

Thank you @kristoferbaxter :)

I'm going to make some additional changes that bring back your dual/native testing, but I don't want to include that noise here.

Appreciate your patience