Add `YAMLParser.Feature.PARSE_BOOLEAN_LIKE_WORDS_AS_STRINGS` to allow parsing "boolean" words as strings instead of booleans

[axelniklasson]

Right now YAMLParser._matchYAMLBoolean provides no flexibility to avoid words that are considered booleans to be parsed as strings instead, which is actually sometimes the desired behaviour and a good candidate for a feature flag in my opinion. I therefore propose the following

• Introduce a new YAMLParser.Feature called PARSE_TRUTHY_WORDS_AS_STRINGS (open for suggestion on names)
• When enabling this flag, the following words (converted to lowercase) will be parsed as strings instead of booleans:
  • yes
  • no
  • on
  • off
  • y
  • n

Note that false and true will still be parsed as booleans.

Let me know what you think! I'll be happy to help out with a PR here.

Related issue: #129

[cowtowncoder]

@axelniklasson Sounds reasonable, I would accept PR and help it get merged. Should go in 2.15 branch (new feature), could make it in 2.15.0 as we'll hope to start release-candidate phase soon.

[axelniklasson]

@cowtowncoder great, thanks for the quick response! I'll get started on the PR today.

[axelniklasson]

@cowtowncoder PR ready here #389, let me know your thoughts!

[cowtowncoder]

Looks pretty good, will add notes over there. Thanks!