Change project dir based on nimgen cfg file

nimgen.nim

@@ -5,7 +5,7 @@ var
   gDoneAfter: seq[string] = @[]
   gDoneInline: seq[string] = @[]
 
-  gProjectDir = getCurrentDir()
+  gProjectDir = ""
   gConfig: Config
   gFilter = ""
   gQuotes = true
@@ -726,6 +726,8 @@ proc runCfg(cfg: string) =
   if not fileExists(cfg):
     raise newException(Exception, "Config doesn't exist: " & cfg)
 
+  gProjectDir = parentDir(cfg)
+
   gConfig = loadConfig(cfg)
 
   if gConfig.hasKey("n.global"):