Adding Functions Used in Line Following

Adding function to make getMainFeatures on LineTracking and getters for the frame height and width from Pixy2.  These are used in line following.

Author: jaredbro

src/main/java/io/github/pseudoresonance/pixy2api/Pixy2.java

@@ -311,6 +311,20 @@ public String getFirmwareTypeString() {
 		}
 	}
 
+	/**
+	 * Get width of the pixy's visual frame after it is calcualted during init
+	 */
+	public int getFrameWidth() {
+		return frameWidth;
+	}
+
+	/**
+	 * Get height of the pixy's visual frame after it is calcualted during inits
+	 */
+ 	public int getFrameHeight() {
+		return frameHeight;
+	}
+
 	/**
 	 * Synchronizes communication with Pixy2
 	 * 

src/main/java/io/github/pseudoresonance/pixy2api/Pixy2Line.java

@@ -87,6 +87,16 @@ public byte getAllFeatures() {
 		return getFeatures(LINE_GET_ALL_FEATURES, LINE_ALL_FEATURES, true);
 	}
 
+	/**
+	 * Gets the main features from the Pixy2.  This is a more constrained line tracking algorithm.
+	 * 
+	 * @return Pixy2 error code
+	 */
+	public byte getMainFeatures()
+  {
+    return getFeatures(LINE_GET_MAIN_FEATURES, LINE_ALL_FEATURES, true); 
+  }
+
 	/**
 	 * Gets specified features from Pixy2
 	 *