dhall-to-yaml and dhall-to-yaml-ng quote inconsistently

[sjakobi]

dhall-yaml
  ./tasty/data/quoted
    HsYAML:     OK
    aeson-yaml: FAIL
      tasty/Main.hs:59:
      Conversion to YAML did not generate the expected output
      expected: "'bool_value': true\n'int_value': 1\n'string_value': '2000-01-01'\n'text': |\n  Plain text\n'yes': 'y'\n"
       but got: "'bool_value': true\n'int_value': 1\n'string_value': \"2000-01-01\"\n'text': |\n  Plain text\n'yes': 'y'\n"

According to @patrickmn, aeson-yaml

single-quote[s] "safe" strings and double-quote unsafe, and number/dates are part of the unsafes.

which seems reasonable to me. So if a fix in aeson-yaml turns out to be very tricky, IMHO we could also try adjusting the HsYAML-based code to follow the same scheme.

[sjakobi]

I have disabled the test for now:

dhall-haskell/dhall-yaml/tasty/Main.hs

Lines 35 to 38 in bbb1ca8

	, Test.Tasty.ExpectedFailure.ignoreTestBecause "#1516" $
	testDhallToYaml
	(Dhall.JSON.Yaml.defaultOptions { quoted = True })
	"./tasty/data/quoted"

[sjakobi]

@patrickmn Did you get a chance to look at this again?

To be clear: I don't actually care whether we quote with single-quotes or double-quotes, but I worry that maintaining both dhall-to-yaml and dhall-to-yaml-ng may become a bit of a headache if their behaviour diverges already so early on!