Start adding DelegatorsParam

- Going to need to work on getting the ability to add with a string
  or a string[]. Might just make it only work with Array and go back
  to clean up the API later.

PROGRESS.md

@@ -261,6 +261,32 @@ the same as they would the UNKNOWN value.
   - `ATTENDEE;CUTYPE=GROUP:mailto:ietf-calsch@example.org`
 
 ### 3.2.4. Delegators
+
+- Purpose: To specify the calendar users that have delegated their
+participation to the calendar user specified by the property.
+
+- Format Definition: This property parameter is defined by the following
+notation:
+
+> ```
+> delfromparam = "DELEGATED-FROM" "=" DQUOTE cal-address
+>                DQUOTE *("," DQUOTE cal-address DQUOTE)
+> ```
+
+- Description: This parameter can be specified on properties with a
+ CAL-ADDRESS value type. This parameter specifies those calendar
+ users that have delegated their participation in a group-scheduled
+ event or to-do to the calendar user specified by the property.
+ The individual calendar address parameter values MUST each be
+ specified in a quoted-string.
+
+- Example:
+
+> ```
+> ATTENDEE;DELEGATED-FROM="mailto:jsmith@example.com":mailto:
+>  jdoe@example.com
+> ```
+
 ### 3.2.5. Delegatees
 ### 3.2.6. Directory Entry Reference
 ### 3.2.7. Inline Encoding

src/DelegatorsParam.ts

+
+/*
+ * lib-ical
+ * Copyright (C) 2017 Mark Stenglein
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published
+ * by the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+import Parameter from "./Parameter";
+
+export default class DelegatorsParam extends Parameter {
+    private _delegators: string[];
+
+    constructor(delegators: string | string[]) {
+        super("DELEGATED-FROM", []);
+        if (Array.isArray(delegators)) {
+            delegators = (delegators instanceof Array) ? delegators : [delegators];
+            this._delegators = this._delegators.concat(<string[]>delegators)
+        }
+    }
+
+    get delegators(): string | string[] {
+        return this._delegators;
+    }
+
+    set delegators(newDelegators: string | string[]) {
+        this._delegators = newDelegators;
+    }
+}