Add Location.setDirection(Vector). Adds BUKKIT-4862

This commit adds an additional method to Location to set the direction of
facing. Included are a set of unit tests that ensure the consistency of
getDirection and setDirection using a set of cardinal directions and
arbituary data points.

Javadocs were also added to pitch and yaw methods that explain the unit
and points of origin.

By: Wesley Wolfe <weswolf@aol.com>

paper-api/src/main/java/org/bukkit/Location.java

@@ -167,45 +167,79 @@ public class Location implements Cloneable {
     }
 
     /**
-     * Sets the yaw of this location
+     * Sets the yaw of this location, measured in degrees.
+     * <ul>
+     * <li>A yaw of 0 or 360 represents the positive z direction.
+     * <li>A yaw of 180 represents the negative z direction.
+     * <li>A yaw of 90 represents the negative x direction.
+     * <li>A yaw of 270 represents the positive x direction.
+     * </ul>
+     * Increasing yaw values are the equivalent of turning to your
+     * right-facing, increasing the scale of the next respective axis, and
+     * decreasing the scale of the previous axis.
      *
-     * @param yaw New yaw
+     * @param yaw new rotation's yaw
      */
     public void setYaw(float yaw) {
         this.yaw = yaw;
     }
 
     /**
-     * Gets the yaw of this location
+     * Gets the yaw of this location, measured in degrees.
+     * <ul>
+     * <li>A yaw of 0 or 360 represents the positive z direction.
+     * <li>A yaw of 180 represents the negative z direction.
+     * <li>A yaw of 90 represents the negative x direction.
+     * <li>A yaw of 270 represents the positive x direction.
+     * </ul>
+     * Increasing yaw values are the equivalent of turning to your
+     * right-facing, increasing the scale of the next respective axis, and
+     * decreasing the scale of the previous axis.
      *
-     * @return Yaw
+     * @return the rotation's yaw
      */
     public float getYaw() {
         return yaw;
     }
 
     /**
-     * Sets the pitch of this location
+     * Sets the pitch of this location, measured in degrees.
+     * <ul>
+     * <li>A pitch of 0 represents level forward facing.
+     * <li>A pitch of 90 represents downward facing, or negative y
+     *     direction.
+     * <li>A pitch of -90 represents upward facing, or positive y direction.
+     * <ul>
+     * Increasing pitch values the equivalent of looking down.
      *
-     * @param pitch New pitch
+     * @param pitch new incline's pitch
      */
     public void setPitch(float pitch) {
         this.pitch = pitch;
     }
 
     /**
-     * Gets the pitch of this location
+     * Sets the pitch of this location, measured in degrees.
+     * <ul>
+     * <li>A pitch of 0 represents level forward facing.
+     * <li>A pitch of 90 represents downward facing, or negative y
+     *     direction.
+     * <li>A pitch of -90 represents upward facing, or positive y direction.
+     * <ul>
+     * Increasing pitch values the equivalent of looking down.
      *
-     * @return Pitch
+     * @return the incline's pitch
      */
     public float getPitch() {
         return pitch;
     }
 
     /**
-     * Gets a Vector pointing in the direction that this Location is facing
+     * Gets a unit-vector pointing in the direction that this Location is
+     * facing.
      *
-     * @return Vector
+     * @return a vector pointing the direction of this location's {@link
+     *     #getPitch() pitch} and {@link #getYaw() yaw}
      */
     public Vector getDirection() {
         Vector vector = new Vector();
@@ -215,14 +249,47 @@ public class Location implements Cloneable {
 
         vector.setY(-Math.sin(Math.toRadians(rotY)));
 
-        double h = Math.cos(Math.toRadians(rotY));
+        double xz = Math.cos(Math.toRadians(rotY));
 
-        vector.setX(-h * Math.sin(Math.toRadians(rotX)));
-        vector.setZ(h * Math.cos(Math.toRadians(rotX)));
+        vector.setX(-xz * Math.sin(Math.toRadians(rotX)));
+        vector.setZ(xz * Math.cos(Math.toRadians(rotX)));
 
         return vector;
     }
 
+    /**
+     * Sets the {@link #getYaw() yaw} and {@link #getPitch() pitch} to point
+     * in the direction of the vector.
+     */
+    public Location setDirection(Vector vector) {
+        /*
+         * Sin = Opp / Hyp
+         * Cos = Adj / Hyp
+         * Tan = Opp / Adj
+         *
+         * x = -Opp
+         * z = Adj
+         */
+        final double _2PI = 2 * Math.PI;
+        final double x = vector.getX();
+        final double z = vector.getZ();
+
+        if (x == 0 && z == 0) {
+            pitch = vector.getY() > 0 ? -90 : 90;
+            return this;
+        }
+
+        double theta = Math.atan2(-x, z);
+        yaw = (float) Math.toDegrees((theta + _2PI) % _2PI);
+
+        double x2 = NumberConversions.square(x);
+        double z2 = NumberConversions.square(z);
+        double xz = Math.sqrt(x2 + z2);
+        pitch = (float) Math.toDegrees(Math.atan(-vector.getY() / xz));
+
+        return this;
+    }
+
     /**
      * Adds the location by another.
      *