added some javadoc

library/src/main/java/org/mustangproject/CashDiscount.java

@@ -4,9 +4,18 @@ import org.mustangproject.ZUGFeRD.IZUGFeRDCashDiscount;
 
 import java.math.BigDecimal;
 
+/***
+ * A class to represent discounts for early payments ("Skonto")
+ */
 public class CashDiscount implements IZUGFeRDCashDiscount {
 
+	/***
+	 * the reduction percent allowed in the period
+	 */
 	protected BigDecimal percent;
+	/***
+	 * the period (usually days) count how long the percent apply
+	 */
 	protected Integer days=null;
 
 	/***
@@ -15,7 +24,7 @@ public class CashDiscount implements IZUGFeRDCashDiscount {
 	 * is be space for a (optional) third parameter
 	 *
 	 * @param percent max 3 decimals "behind the dot", more precision is currently ignored
-	 * @param days
+	 * @param days the count of the periods (usually days) the percentage applies
 	 */
 	public CashDiscount(BigDecimal percent, int days) {
 		this.percent = percent;

library/src/main/java/org/mustangproject/Invoice.java

@@ -578,7 +578,7 @@ public class Invoice implements IExportableTransaction {
 	}
 	/***
 	 * Adds a cash discount (skonto)
-	 * @param CashDiscount the percent/period combination
+	 * @param c the CashDiscount percent/period combination
 	 * @return fluent setter
 	 */
 	public Invoice addCashDiscount(CashDiscount c) {

library/src/main/java/org/mustangproject/TradeParty.java

@@ -423,8 +423,9 @@ public class TradeParty implements IZUGFeRDExportableTradeParty {
 
 
 	/***
-	 * sets the email of the organization (not the one of the contact person)
-	 * (while setEmail has to be defined here getEmail comes from IZUGFeRDExportableTradeParty)
+	 * 	sets the email of the organization (not the one of the contact person)
+	 * 	(while setEmail has to be defined here getEmail comes from IZUGFeRDExportableTradeParty)
+	 * @param eMail address of institution (not contact)
 	 * @return fluent setter
 	 */
 	public TradeParty setEmail(String eMail) {