Add rm utility and improve further

cat.nim

@@ -1,15 +1,26 @@
 import cligen, os, streams
 import common
 
+proc catFile(file:string) =
+    if not existsFile(file):
+        echo "cat: " & file & ": No such file or directory"
+        return
+    var s = newFileStream(file, fmRead)
+    while not s.atEnd:
+        write(stdout, s.readChar)
+
+proc catStdin() =
+    var line = ""
+    while stdin.readLine(line):
+        echo line
+
 proc main(files:seq[string]) =
+    if files.len == 0:
+        catStdin()
     for file in files:
         if file == "-":
-            var line = ""
-            while stdin.readLine(line):
-                echo line
+            catStdin()
         else:
-            var s = newFileStream(file, fmRead)
-            while not s.atEnd:
-                write(stdout, s.readChar)
+            catFile(file)
 
 dispatch(main, version=("version", nimbaseVersion))