Allow $refs to link Objects

[MikeRalphson]

• Addresses Re-usable links not linting #21
• Backports the fix from swagger2openapi
• Also include if !/else reworks to quiet eslint

Have PR'd this rather than applying directly, so a) it can get an approval first, b) we might want more tests and c) because I'm seeing four test failures (unchanged before and after this patch).

  19 passing (83ms)
  4 failing

  1) loadSpec()
       loads yaml specs:
     OpenError: ENOENT: no such file or directory, open '/home/mike/nodejs/speccy/test/samples/openapi.yaml'
      at readSpecFile.then.err (lib/loader.js:70:27)
      at <anonymous>

  2) loadSpec()
       does not resolve references by default:
     OpenError: ENOENT: no such file or directory, open '/home/mike/nodejs/speccy/test/samples/refs/openapi.yaml'
      at readSpecFile.then.err (lib/loader.js:70:27)
      at <anonymous>

  3) loadSpec()
       resolves refs when passed { resolve: true }:
     OpenError: ENOENT: no such file or directory, open '/home/mike/nodejs/speccy/test/samples/refs/openapi.yaml'
      at readSpecFile.then.err (lib/loader.js:70:27)
      at <anonymous>

  4) loadSpec()
       throws ReadError for invalid YAML/JSON:

      AssertionError: expected 'OpenError' to be 'ReadError'
      + expected - actual

      -OpenError
      +ReadError
      
      at Assertion.fail (node_modules/should/cjs/should.js:275:17)
      at Assertion.value (node_modules/should/cjs/should.js:356:19)
      at Context.it (test/loader.test.js:49:34)
      at <anonymous>

[philsturgeon]

Ah, yep, that's on me. The .gitignore has some rules in it which speccy does not need, and I didn't remove them. We're missing some spec files that tests need, and they're on my laptop at the office: on the other size of Storm Skylar.

I'll merge this with failing tests, and have a PR ready to sort that out by this evening.