parser should accept only instances of LocalDate and reject JS Dates

[FrancescoCioria]

requirements

parser should accept only instances of LocalDate and reject JS Dates because we want to be sure that users are aware that passing as ISO date to LocalDate gives a different result than passing it to a Date.

Nevertheless, we should keep accepting instances of LocalDate so to give a way to easily clone a LocalDate

specs

parser should accept only undefined, instances of LocalDate and ISO dates:

• add if (typeof value === 'undefined') to handle first case
• replace instanceof Date with instanceof LocalDate
• ISO dates should be already fine

misc

{optional: other useful info}