Add pwd utility and performance to cat

cat.nim

@@ -3,11 +3,19 @@ import common
 
 proc catFile(file:string) =
     if not existsFile(file):
-        echo "cat: " & file & ": No such file or directory"
+        err "cat: " & file & ": No such file or directory"
         system.quit 1
-    var s = newFileStream(file, fmRead)
-    while not s.atEnd:
-        write(stdout, s.readChar)
+    const bufSize = 1024
+    var
+        f = open(file, fmRead)
+        buffer {.noinit.}: array[bufSize, char]
+    while true:
+        let readBytes = readBuffer(f, addr(buffer[0]), bufSize)
+        if readBytes == 0:
+            break
+        discard writeBuffer(stdout, addr(buffer[0]), readBytes)
+        if readBytes < bufSize:
+            break
 
 proc catStdin() =
     var line = ""