Nice things (test refactor) from PR 39

[warpech]

PR #39 contains discussable changes that downgrade performance, but also refactoring of the test suite.

Since I don't want to merge performance degradation until absolutely required, I decided to make another PR with things that are easier to agree with.

In fact, these changes were already agreed, because PR #39 got a green light for merging. Just in case, @tomalec please give a quick review again. Changes are only in package.json and tests.

Changes are explained in the commit messages, but here's a short summary:

• DRY-er unit tests and benchmark suites
• more meaningful benchmark suites (e.g. for getting data from the observed object)
• old command npm run bench does not compare with fast-json-patch anymore
• new command npm run bench-compare compares with fast-json-patch and no-op

I think this can be merged to master before PRs #39 and #41, then I can open new rebased PRs for #39 and #41 (this won't take long).

Benchmark formatting before this PR:

jsonpatcherproxy generate operation
 Ops/sec: 144269 ±2.90% Ran 9277 times in 0.064 seconds.
jsonpatch generate operation
 Ops/sec: 97748 ±7.24% Ran 6095 times in 0.062 seconds.
jsonpatcherproxy mutation - huge object
 Ops/sec: 790 ±3.76% Ran 50 times in 0.063 seconds.
jsonpatch mutation - huge object
 Ops/sec: 761 ±2.86% Ran 45 times in 0.059 seconds.
jsonpatcherproxy generate operation - huge object
 Ops/sec: 708 ±4.18% Ran 46 times in 0.065 seconds.
jsonpatch generate operation - huge object
 Ops/sec: 851 ±1.40% Ran 47 times in 0.055 seconds.
PROXIFY big object
 Ops/sec: 1805 ±2.05% Ran 104 times in 0.058 seconds.
DIRTY-OBSERVE big object
 Ops/sec: 1697 ±1.17% Ran 93 times in 0.055 seconds.

Benchmark formatting after this PR:

Observe and generate, small object (noop)
 Ops/sec: 12434413 ±0.39% Ran 637179 times in 0.051 seconds.
Observe and generate, small object (JSONPatcherProxy)
 Ops/sec: 95511 ±2.74% Ran 5983 times in 0.063 seconds.
Observe and generate, small object (fast-json-patch)
 Ops/sec: 68608 ±1.63% Ran 3780 times in 0.055 seconds.
Observe and generate (noop)
 Ops/sec: 164602 ±0.30% Ran 8453 times in 0.051 seconds.
Observe and generate (JSONPatcherProxy)
 Ops/sec: 1893 ±1.92% Ran 204 times in 0.108 seconds.
Observe and generate (fast-json-patch)
 Ops/sec: 1650 ±0.98% Ran 95 times in 0.058 seconds.
Primitive mutation (noop)
 Ops/sec: 2601631 ±0.32% Ran 132729 times in 0.051 seconds.
Primitive mutation (JSONPatcherProxy)
 Ops/sec: 524799 ±0.19% Ran 26797 times in 0.051 seconds.
Primitive mutation (fast-json-patch)
 Ops/sec: 7955 ±0.36% Ran 409 times in 0.051 seconds.
Complex mutation (noop)
 Ops/sec: 6382115 ±0.23% Ran 325296 times in 0.051 seconds.
Complex mutation (JSONPatcherProxy)
 Ops/sec: 8731 ±0.30% Ran 448 times in 0.051 seconds.
Complex mutation (fast-json-patch)
 Ops/sec: 8281 ±0.26% Ran 424 times in 0.051 seconds.
Serialization (noop)
 Ops/sec: 7036 ±0.38% Ran 365 times in 0.052 seconds.
Serialization (JSONPatcherProxy)
 Ops/sec: 1278 ±0.34% Ran 66 times in 0.052 seconds.
Serialization (fast-json-patch)
 Ops/sec: 7092 ±0.49% Ran 365 times in 0.051 seconds.