Allow after/before modifiers into a same object

[gpbl]

There's some confusion about using the { before }/{ after } modifiers (e.g. #352 and #324):

// not working
disabledDays={ { before: aDate, after: aDate }}
//  working
disabledDays={ [ { before: aDate}, { after: aDate }] }

The first is indeed more logic...

• update code to work with { before, after } modifiers
• update docs
• update typescript definitions