Update date documentation

Sources/SwiftKit/Date/Date+Difference.swift

@@ -10,30 +10,51 @@ import Foundation
 
 public extension Date {
     
+    /**
+     The number of years between this date and another one.
+     */
     func years(from date: Date, calendar: Calendar = .current) -> Int {
         calendar.dateComponents([.year], from: date, to: self).year ?? 0
     }
     
+    /**
+     The number of months between this date and another one.
+     */
     func months(from date: Date, calendar: Calendar = .current) -> Int {
         calendar.dateComponents([.month], from: date, to: self).month ?? 0
     }
     
+    /**
+     The number of weeks between this date and another one.
+     */
     func weeks(from date: Date, calendar: Calendar = .current) -> Int {
         calendar.dateComponents([.weekOfYear], from: date, to: self).weekOfYear ?? 0
     }
     
+    /**
+     The number of days between this date and another one.
+     */
     func days(from date: Date, calendar: Calendar = .current) -> Int {
         calendar.dateComponents([.day], from: date, to: self).day ?? 0
     }
     
+    /**
+     The number of hours between this date and another one.
+     */
     func hours(from date: Date, calendar: Calendar = .current) -> Int {
         calendar.dateComponents([.hour], from: date, to: self).hour ?? 0
     }
     
+    /**
+     The number of minutes between this date and another one.
+     */
     func minutes(from date: Date, calendar: Calendar = .current) -> Int {
         calendar.dateComponents([.minute], from: date, to: self).minute ?? 0
     }
     
+    /**
+     The number of seconds between this date and another one.
+     */
     func seconds(from date: Date, calendar: Calendar = .current) -> Int {
         calendar.dateComponents([.second], from: date, to: self).second ?? 0
     }

Sources/SwiftKit/Date/Date+Init.swift

@@ -10,6 +10,10 @@ import Foundation
 
 public extension Date {
     
+    /**
+     Create a date value using the provided components. Year,
+     month and day are required, while the others are not.
+     */
     init?(
         year: Int,
         month: Int,

Sources/SwiftKit/Date/DateDecoders.swift

@@ -23,6 +23,11 @@ public extension JSONDecoder {
 
 private extension JSONDecoder.DateDecodingStrategy {
     
+    /**
+     This strategy can be used to parse ISO8601 dates. It is
+     more robust than the standard strategy, and will try to
+     parse both milliseconds and seconds.
+     */
     static let robustISO8601 = custom { decoder throws -> Date in
         let container = try decoder.singleValueContainer()
         let string = try container.decode(String.self)

Sources/SwiftKit/Date/DateFormatters.swift

@@ -10,6 +10,10 @@ import Foundation
 
 public extension DateFormatter {
     
+    /**
+     Create a custom date formatter, that uses a custom date
+     format, calendar, locale and time zone.
+     */
     convenience init(
         dateFormat: String,
         calendar: Calendar = Calendar(identifier: .iso8601),