Implement sin function and helper functions such as getSmallAngle and floor.

src/main/java/org/nwapw/abacus/number/NumberInterface.java

@@ -85,6 +85,12 @@ public interface NumberInterface {
      */
     int ceiling();
 
+    /**
+     * Return the greatest integer less than or equal to the number.
+     * @return the greatest int >= the number, if int can hold the value.
+     */
+    int floor();
+
     /**
      * Promotes this class to another number class.
      *