Use eslint-config-metarhia

[aqrln]

This commit removes .eslintrc.yml in favor of using the
eslint-config-metarhia package. Three rules are turned off here,
because they trigger lots of linter errors:

• arrow-parens — forces consistent parens usage in arrow functions
• comma-dangle — forces VCS- and diff-friendly comma usage
• handle-callback-err — ensures the errors are handled instead of
  being silently ignored

How these exceptions are handled further is outside the scope of this
commit/pull request, and they might need somewhat deeper investigation
than just considering the rules themselves. E.g., errors triggered by
handle-callback-err may not necessarily mean that there's a lot of
places errors are not handled in metasync (though if that's indeed the
case, it will show nicely where to fix these bugs so that one doesn't
need to spot all of them manually), but it might be just that there's
some trouble with regex specified in this rule's settings.

One of the linter errors is handled in this commit though: there was a
require() call pointing to a non-existent file, which is now fixed.

Also, eslint package has been updated to match what peerDependencies
of eslint-config-metarhia require, and eslint-plugin-import, which
is also a part of the config's peerDependencies, has been installed.

[aqrln]

I've taken another look, and yeah, handle-callback-err failures are legitimate, but all of them are in tests, not in the library code itself. I'd say land this as-is, and then remove "handle-callback-err": "off" from .eslintrc.json and add test.notOk(error, 'operation must not return an error'); where necessary as a separate commit.

[belochub]

Closed in favor of #379.