classes for today, weekend dates; limitation to min/max dates; export css prefix prop

[denisvmedia]

New properties added:

    weekendDays: [Array], // array of week day numbers 0..6 (by default [0, 6] - sunday and saturday)
    pre: [String],        // css prefix (by default "calendar")
    minDate: [Date],      // min date that can be selected in the calendar (will also limit month navigation)
    maxDate: [Date],      // max date that can be selected in the calendar (will also limit month navigation)

New classes added:

calendar-date-weekend - weekend day defined by weekendDays calendar-date-today - defines today date

[denisvmedia]

Hope, we can merge it :)