Yams.dump dumps numerical String values as Number

[jaynetics]

this seems to be similar to #174 though i'm not sure it's the same issue.

let dict = ["1.0": "2."]
print(try! Yams.dump(object: dict))

expected output: '1.0': '2.'
actual output: 1.0: 2.

maybe this is an accepted limitation?

if so, i'd love to know if there is a sane way to correctly dump dicts of an unknown structure. i can only think of deep-mapping them to Nodes and setting styles based on the Strings' contents...

[norio-nomura]

If Resolver.default determines that the content of String is other than .str, it would be better to apply Style.singleQuoted to Node.Scalar on representing from that String.