Merge pull request #1986 from BlythMeister/logging

Add traceImportant and traceError with formats

src/app/Fake.Core.Trace/Trace.fs

@@ -44,12 +44,18 @@ let traceVerbose s =
 /// Writes a trace to stderr (in yellow)  
 let traceImportant text = CoreTracing.postMessage (TraceData.ImportantMessage text)
 
+/// Writes a message to stderr (in yellow) 
+let traceImportantfn fmt = Printf.ksprintf traceImportant fmt
+
 /// Writes a trace to the command line (in yellow)
 let traceFAKE fmt = Printf.ksprintf (TraceData.ImportantMessage >> CoreTracing.postMessage) fmt
 
 /// Traces an error (in red)
 let traceError error = CoreTracing.postMessage (TraceData.ErrorMessage error)
 
+/// Writes an error message to stderr (in red) 
+let traceErrorfn fmt = Printf.ksprintf traceError fmt
+
 open Microsoft.FSharp.Core.Printf
 
 /// Converts an exception and its inner exceptions to a nice string.