Implement date-related java.time classes

Implement `java.time.Period`, `java.time.LocalDate`,
`java.time.DayOfWeek` and `java.time.Month` as well as
most classes in `java.time.chrono`.
Also add more tests for existing `java.time` classes.

Author: ummels

src/main/scala/java/time/DayOfWeek.scala

@@ -0,0 +1,79 @@
+package java.time
+
+import java.time.temporal._
+
+final class DayOfWeek private (name: String, value: Int)
+    extends Enum[DayOfWeek](name, value - 1) with TemporalAccessor
+    with TemporalAdjuster {
+
+  def getValue(): Int = value
+
+  // Not implemented
+  // def getDisplayName(style: TextStyle, locale: ju.Locale): String
+
+  def isSupported(field: TemporalField): Boolean = field match {
+    case _: ChronoField  => field == ChronoField.DAY_OF_WEEK
+    case null            => false
+    case _               => field.isSupportedBy(this)
+  }
+
+  // Implemented by TemporalAccessor
+  // def range(field: TemporalField): ValueRange
+
+  // Implemented by TemporalAccessor
+  // def get(field: TemporalField): Int
+
+  def getLong(field: TemporalField): Long = field match {
+    case ChronoField.DAY_OF_WEEK => ordinal + 1
+
+    case _: ChronoField =>
+      throw new UnsupportedTemporalTypeException(s"Field not supported: $field")
+
+    case _ => field.getFrom(this)
+  }
+
+  def plus(days: Long): DayOfWeek = {
+    val offset = (days % 7 + 7) % 7
+    DayOfWeek.of((ordinal + offset.toInt) % 7 + 1)
+  }
+
+  def minus(days: Long): DayOfWeek = plus(-(days % 7))
+
+  // Not implemented
+  // def query[R](query: TemporalQuery[R]): R
+
+  def adjustInto(temporal: Temporal): Temporal =
+    temporal.`with`(ChronoField.DAY_OF_WEEK, ordinal + 1)
+}
+
+object DayOfWeek {
+  final val MONDAY = new DayOfWeek("MONDAY", 1)
+
+  final val TUESDAY = new DayOfWeek("TUESDAY", 2)
+
+  final val WEDNESDAY = new DayOfWeek("WEDNESDAY", 3)
+
+  final val THURSDAY = new DayOfWeek("THURSDAY", 4)
+
+  final val FRIDAY = new DayOfWeek("FRIDAY", 5)
+
+  final val SATURDAY = new DayOfWeek("SATURDAY", 6)
+
+  final val SUNDAY = new DayOfWeek("SUNDAY", 7)
+
+  private val days =
+    Seq(MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY)
+
+  def values(): Array[DayOfWeek] = days.toArray
+
+  def valueOf(name: String): DayOfWeek = days.find(_.name == name).getOrElse {
+    throw new IllegalArgumentException(s"No such weekday: $name")
+  }
+
+  def of(dayOfWeek: Int): DayOfWeek = days.lift(dayOfWeek - 1).getOrElse {
+    throw new DateTimeException(s"Invalid value for weekday: $dayOfWeek")
+  }
+
+  def from(temporal: TemporalAccessor): DayOfWeek =
+    DayOfWeek.of(temporal.get(ChronoField.DAY_OF_WEEK))
+}