Document integration with plogr

[krlmlr]

• Make sure that enabling/disabling of {plogr} is consistent with the {debugme} strategy
• Make {plogr} use the same output routine
• Show a worked example
• Document

[gaborcsardi]

I realize this is probably not happening any time soon, but we can keep this open, just like we keep other debugme issues open, because IMO we do need something like debugme, just a better, more robust implementation.