Support `date` and `datetime` data type

[techniq]

Extracted from https://github.com/techniq/odata-query/pull/20#issuecomment-407770014

Regarding dates and times they do not appear to qualify the values with a type except optionally with a duration.

DateValue eq 2012-12-03
DateTimeOffsetValue eq 2012-12-03T07:16:23Z
DurationValue eq duration'P12DT23H59M59.999999999999S'
DurationValue eq 'P12DT23H59M59.999999999999S'
TimeOfDayValue eq 07:59:59.999

We could support the following in handleValue

• { type: 'datetimeoffset', value: date } and a Date instance (like we do now):
  • date.toISOString() => 2012-12-03T07:16:23Z
• { type: 'date', value: date }:
  • date.toISOString().split('T')[0] => 2012-12-03

We should also support date as either a Date instance or a string (ex. 2018-01-02):

const dateValue = (typeof date === 'string') ? new Date(date) : date instanceof Date ? date : null
const value = dateValue && dateValue.toISOString();

[samuelportz]

I think it would be nice also to accept integer, when a type is given.

let dateValue = null;
switch (typeof value) {
    case 'string':
    case 'number':
        dateValue = new Date(value).toISOString();
        break;
    case 'object':
        if (value instanceof Date) dateValue = value.toISOString();
        break;
}