Move MarkerGson into its own package

Author: TBlueF

src/main/java/de/bluecolored/bluemap/api/markers/MarkerGson.java renamed to src/main/java/de/bluecolored/bluemap/api/gson/MarkerGson.java

@@ -22,7 +22,7 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
-package de.bluecolored.bluemap.api.markers;
+package de.bluecolored.bluemap.api.gson;
 
 import com.flowpowered.math.vector.Vector2d;
 import com.flowpowered.math.vector.Vector2i;
@@ -32,6 +32,7 @@
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonToken;
 import com.google.gson.stream.JsonWriter;
+import de.bluecolored.bluemap.api.markers.*;
 import de.bluecolored.bluemap.api.math.Color;
 import de.bluecolored.bluemap.api.math.Line;
 import de.bluecolored.bluemap.api.math.Shape;