This patch adds a few extra reader features which would allow the reader to accept non-standard, but somewhat common JSON strings. In particular:
1) Features::allowDroppedNullPlaceholders_ will accept JSON with 'null' tokens that have been stripped. The writer already has an option for creating JSON without nulls. This would provide parity between the two.
2) Features::allowNumericKeys_ will accept JSON where the objects may have numeric keys in addition to the standard string keys.
I've currently made these both default to false, even in Features::all() which says that it allows all features. Please feel free to change this if you think it should use these as well.