SAS date formats implementation (#86)

* Implemented sas date formats

src/main/java/com/epam/parso/date/NotImplementedException.java

@@ -0,0 +1,9 @@
+package com.epam.parso.date;
+
+/**
+ * Declared but not yet implemented formats throw this type of exception.
+ * This exception is suppose to be caught internally to substitute
+ * not implemented with on of fallback date format.
+ */
+class NotImplementedException extends RuntimeException {
+}

src/main/java/com/epam/parso/date/OutputDateType.java

@@ -15,6 +15,20 @@ public enum OutputDateType {
      * can't be represented as a LocalTime!
      */
     JAVA_TEMPORAL,
+    /**
+     * Output date as String formatted according to
+     * column format defined in the source SAS file.
+     * <p>
+     * Not all formats are yet supported and there is a slight difference
+     * between SAS and Parso results (at least in rounding),
+     * so this option is marked as experimental.
+     */
+    SAS_FORMAT_EXPERIMENTAL,
+    /**
+     * Same as SAS_FORMAT, but result doesn't have leading spaces
+     * (trimmed, as the SAS Universal Viewer outputs by default).
+     */
+    SAS_FORMAT_TRIM_EXPERIMENTAL,
     /**
      * Output date as raw SAS value.
      * It is number of days (for date type) or seconds(for datetime type)