Add YAMLParser.Feature.PARSE_BOOLEAN_LIKE_WORDS_AS_STRINGS to allow disabling of coercion of Boolean-like Strings

[axelniklasson]

Introduce a new feature flag to YAMLParser that when explicitly enabled, leads to the following words (irrespective of case) being parsed as strings instead of booleans:

• yes
• no
• off
• on

Note that y/n are already parsed as strings and this change will not impact how true and false are being parsed - they will still be parsed as booleans.

Fixes #388

[cowtowncoder]

Ok I think this looks fine on first look (I'll need to go over it once more before merging just in case but nothing off so far). So I think I'd like to get it merged.

But one (and only) process thing: if I haven't asked for and gotten CLA:

https://github.com/FasterXML/jackson/blob/master/contributor-agreement.pdf

yet, it'd be needed before the first contribution (and it's then good for any number of contributions to Jackson project).

The usual way is to print it, fill & sign, scan/photo, email to info at fasterxml dot com.

Once I get that I can proceed with merging.

Thank you for this contribution & looking forward to merging it!

[axelniklasson]

Thanks for looking @cowtowncoder! Added the @since tag and sent over the signed CLA as well.

[cowtowncoder]

CLA received, doing last review now.

[cowtowncoder]

I'll change this to use builder-based configuration, merges more cleanly in master (3.0 has immutable factories).

[axelniklasson]

Thanks for the quick turnaround @cowtowncoder, happy to see this merged! Do you by any chance have a rough timeline for when 2.15 might be available?

[cowtowncoder]

@axelniklasson Hoping to get release candidate out in early March (in 2 weeks?), and from that, 3-4 weeks for final release.