Allow custom layout renderers to use stacktrace
Allow custom layout renderers to use stacktrace

Be deriving from IUsesStackTrace custom layout renderers can get
stacktrace information from log messages.
closes #295

AqlaSolutions/NLog-Unity3D,zbrad/NLog,rajk987/NLog,babymechanic/NLog,sean-gilliam/NLog,rajk987/NLog,czema/NLog,thomkinson/NLog,bhaeussermann/NLog,rajeshgande/NLog,pwelter34/NLog,vladikk/NLog,kevindaub/NLog,MartinTherriault/NLog,fringebits/NLog,ie-zero/NLog,breyed/NLog,hubo0831/NLog,ajayanandgit/NLog,campbeb/NLog,ajayanandgit/NLog,rajeshgande/NLog,MoaidHathot/NLog,fringebits/NLog,FeodorFitsner/NLog,matteobruni/NLog,zbrad/NLog,czema/NLog,breyed/NLog,rajk987/NLog,thomkinson/NLog,bryjamus/NLog,czema/NLog,AndreGleichner/NLog,AqlaSolutions/NLog-Unity3D,BrandonLegault/NLog,BrandonLegault/NLog,bhaeussermann/NLog,mikkelxn/NLog,vladikk/NLog,thomkinson/NLog,Niklas-Peter/NLog,nazim9214/NLog,NLog/NLog,luigiberrettini/NLog,matteobruni/NLog,MoaidHathot/NLog,bjornbouetsmith/NLog,littlesmilelove/NLog,MartinTherriault/NLog,RichiCoder1/NLog,kevindaub/NLog,Niklas-Peter/NLog,RRUZ/NLog,michaeljbaird/NLog,bjornbouetsmith/NLog,tetrodoxin/NLog,BrandonLegault/NLog,vladikk/NLog,littlesmilelove/NLog,czema/NLog,ilya-g/NLog,ArsenShnurkov/NLog,tetrodoxin/NLog,BrandonLegault/NLog,tohosnet/NLog,BrutalCode/NLog,vladikk/NLog,AqlaSolutions/NLog-Unity3D,snakefoot/NLog,BrutalCode/NLog,304NotModified/NLog,luigiberrettini/NLog,RRUZ/NLog,hubo0831/NLog,mikkelxn/NLog,nazim9214/NLog,pwelter34/NLog,rajk987/NLog,vbfox/NLog,mikkelxn/NLog,tmusico/NLog,AqlaSolutions/NLog-Unity3D,campbeb/NLog,UgurAldanmaz/NLog,babymechanic/NLog,ilya-g/NLog,FeodorFitsner/NLog,fringebits/NLog,mikkelxn/NLog,AndreGleichner/NLog,tohosnet/NLog,ie-zero/NLog,bryjamus/NLog,vbfox/NLog,ArsenShnurkov/NLog,thomkinson/NLog,UgurAldanmaz/NLog,tmusico/NLog,michaeljbaird/NLog,RichiCoder1/NLog,fringebits/NLog