Add indent option to writeGPX()

[bmy4415]

Hi,

I think it is really great if we can use indent optionally.
I found code block https://github.com/himanshu-soni/gpx-parser/blob/master/src/main/java/me/himanshusoni/gpxparser/GPXWriter.java#L74-L80

I think we can easily add next 2 lines to use indent.

transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", Integer.toString(indent));

Here is the post I referenced

• https://www.tabnine.com/code/java/methods/javax.xml.transform.Transformer/setOutputProperty

Thanks for your consideration in advance!
Jaewan