Add clear function to the Printer

clearing terminal is now a function of class  Printer.
Command clear, now use it.

cccli/commands/shell.py

@@ -52,7 +52,7 @@ class Command_clear(Command):
     def __call__(self, argv):
         if len(argv) != 1:
             raise cmdBadArgument()
-        self.printer.out("\033[H\033[2J", nl="")
+        self.printer.clear()
 
 
 class Command_help(Command):

cccli/printer.py

@@ -170,6 +170,12 @@ class Printer(object):
         rows, cols, px_x, px_y = struct.unpack("HHHH", resp)
         return rows, cols
 
+    def clear(self):
+        '''Clear the terminal'''
+        if self.readline is None or not sys.stdout.isatty():
+            return
+        self.out("\033[H\033[2J", nl="")
+
 
 class History(object):
     '''History class'''