Support for empty schemas #255

[sinclairzx81]

This PR adds support for empty {} any schemas to resolve issue #255. This update checks for the existence of a type property on the schema, and if not found, defaults to a JSON.stringify() for serialization.

Have added a few tests to any.test.js and updated index.d.ts accordingly. Submitting this PR for review.

benchmark

cpu  AMD Ryzen 7 3700X 8-Core Processor
ram  32GB 
node v12.18.2

FJS creation x 56,104 ops/sec ±0.26% (92 runs sampled)
CJS creation x 162,430 ops/sec ±0.27% (98 runs sampled)

JSON.stringify array x 3,320 ops/sec ±0.33% (91 runs sampled)
fast-json-stringify array x 8,465 ops/sec ±0.37% (90 runs sampled)

compile-json-stringify array x 7,756 ops/sec ±0.75% (94 runs sampled)
JSON.stringify long string x 10,028 ops/sec ±0.17% (95 runs sampled)

fast-json-stringify long string x 10,098 ops/sec ±0.13% (96 runs sampled)
compile-json-stringify long string x 10,108 ops/sec ±0.10% (99 runs sampled)

JSON.stringify short string x 8,700,507 ops/sec ±0.46% (91 runs sampled)
fast-json-stringify short string x 47,164,570 ops/sec ±0.21% (96 runs sampled)

compile-json-stringify short string x 40,127,602 ops/sec ±0.38% (97 runs sampled)
JSON.stringify obj x 1,827,988 ops/sec ±0.12% (96 runs sampled)

fast-json-stringify obj x 17,418,215 ops/sec ±0.39% (95 runs sampled)
compile-json-stringify obj x 24,095,360 ops/sec ±0.23% (95 runs sampled)

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[fox1t]

LGTM

[L2jLiga]

LGTM

[mcollina]

cc @jsumners

[mcollina]

lgtm

[sinclairzx81]

@mcollina thanks :)