clear screen on windows during Screen.enter.

lib/widget.js

@@ -12,7 +12,8 @@ var EventEmitter = require('./events').EventEmitter
   , assert = require('assert')
   , path = require('path')
   , util = require('util')
-  , fs = require('fs');
+  , fs = require('fs')
+  , cp = require('child_process');
 
 var colors = require('./colors')
   , program = require('./program')
@@ -448,6 +449,13 @@ Screen.prototype.enter = function() {
       this.cursorColor(this.cursor.color);
     }
   }
+  if (process.platform === 'win32') {
+    try {
+      cp.execSync('cls', { stdio: 'ignore', timeout: 1000 });
+    } catch (e) {
+      ;
+    }
+  }
   this.program.alternateBuffer();
   this.program.put.keypad_xmit();
   this.program.csr(0, this.height - 1);