WorldBorder addition and changed to clear confusion

Added new method to set the startingDiameter, endDiameter and the time it will take [void setDiameter(double startDiameter, double endDiameter, long time);]
Changed Radius to Diameter.
Changed get/setBlockBuffer to get/setBuffer and changed the return and parameter to double as it is not measured in whole blocks.
Why did you add this? This is not needed, the next paragraph is wrapped in `<p>` and `</p>`, therefore this will just create additional space between them.