makes new hash the default, with an opt-out (& js-no-big-int) define.
Also update changelog (& fix one typo).
Only really expect the chronos hash-order sensitive test to fail until
they merge that PR and tag a new release.
Prefer moving tests to a non-js directory so that they get tested across all backends automatically.
Ideally, tests/js should be reserved to code that only makes sense in js.
Note also that tests for a js specific module (e.g.: std/jsbigints) belong to tests/stdlib, (e.g.: tests/stdlib/tjsbigints.nim)