Add dbg-macro to coding guide

[gdevenyi]

Via HN: https://github.com/sharkdp/dbg-macro

Single header debugging macro.

[thewtex]

@gdevenyi cool!

Perhaps we should include this in the ITKCommon module, and include it in itk.Macro.h so it is always available.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. Thank you for your contributions.