Allow false (and/or perhaps undefined) values for boolean options

[cvrebert]

Use case: When merging multiple sets of options (e.g. per-file overrides) and you need to relax an option. Currently, using false or undefined in an overriding set of options results in errors, e.g.:

requireCamelCaseOrUpperCaseIdentifiers option requires true value or should be removed
requireCamelCaseOrUpperCaseIdentifiers option requires boolean value

(This is an intentional duplicate of #255, which was prematurely closed.)

[mikesherov]

@cvrebert can you use null? We reserved false and true for future configuration changes. Does null work?

[cvrebert]

Yes, it does! Hadn't thought to try it. Would be nice if that was documented more clearly.
Thanks!

[mikesherov]

@cvrebert yeah, we need to do a better job documenting and making options easier to configure. It's the next big thing we're working on. Thanks for bearing with us!