Show output for the compiler/docgen commands. Fixes #303.

src/nimble.nim

@@ -657,7 +657,7 @@ proc execBackend(options: Options) =
     display("Generating", ("documentation for $1 (from package $2) using $3 " &
             "backend") % [bin, pkgInfo.name, backend], priority = HighPriority)
   doCmd("\"" & getNimBin() & "\" $# --noNimblePath $# \"$#\"" %
-        [backend, args, bin])
+        [backend, args, bin], showOutput = true)
   display("Success:", "Execution finished", Success, HighPriority)
 
 proc search(options: Options) =

src/nimblepkg/tools.nim

@@ -11,7 +11,7 @@ proc extractBin(cmd: string): string =
   else:
     return cmd.split(' ')[0]
 
-proc doCmd*(cmd: string) =
+proc doCmd*(cmd: string, showOutput = false) =
   let bin = extractBin(cmd)
   if findExe(bin) == "":
     raise newException(NimbleError, "'" & bin & "' not in PATH.")
@@ -24,7 +24,10 @@ proc doCmd*(cmd: string) =
   let (output, exitCode) = execCmdEx(cmd)
   displayDebug("Finished", "with exit code " & $exitCode)
   # TODO: Improve to show output in real-time.
-  displayDebug("Output", output)
+  if showOutput:
+    display("Output:", output, priority = HighPriority)
+  else:
+    displayDebug("Output", output)
 
   if exitCode != QuitSuccess:
     raise newException(NimbleError,