Implements SwiftDate/malcommac#780

Author: Sam-Spencer

Sources/SwiftDate/Date/Date+Math.swift

@@ -16,21 +16,31 @@ import Foundation
 /// Follows this mathematical pattern:
 ///     let difference = lhs - rhs
 ///     rhs + difference = lhs
+///
 public func - (lhs: Date, rhs: Date) -> DateComponents {
     SwiftDate.defaultRegion.calendar.dateComponents(DateComponents.allComponentsSet, from: rhs, to: lhs)
 }
 
 /// Adds date components to a date and returns a new date.
+///
 public func + (lhs: Date, rhs: DateComponents) -> Date {
     rhs.from(lhs)!
 }
 
 /// Adds date components to a date and returns a new date.
+///
 public func + (lhs: DateComponents, rhs: Date) -> Date {
     (rhs + lhs)
 }
 
+/// Adds ``DateInRegion`` to a date and returns a new date.
+///
+public func + (lhs: Date, rhs: DateInRegion) -> Date {
+    return (lhs + rhs.date.dateComponents)
+}
+
 /// Subtracts date components from a date and returns a new date.
+///
 public func - (lhs: Date, rhs: DateComponents) -> Date {
     (lhs + (-rhs))
 }