Add `vorpal.ui.clear` command to API

hi, I implemented a clear command in one of my vorpal application following your answers in this post http://stackoverflow.com/questions/8813142/clear-terminal-window-in-node-js-readline-shell/32871585#32871585?newreg=0fd7e6b366544c72b82496cd4c077973

The problem is that the cursor lost in the console after executing the clear command, as the screenshots below:

Before clear,

After clear,

Notice that the grey cursor had gone.

[eistaa]

@mamboer: It’s ANSI escape codes. A breakdown of \u001b[2J\u001b[0;0H is:

• \u001b is the escape character, together with [ it becomes a Control Sequence Introducer (CSI)
• CSI 2J is the sequence for clearing the entire screen
• CSI 0;0H is the sequence for moving the cursor to row 0, column 0

[Maxtoros]

Hey guys am using this command to ‘clean’ the screen , especially after a messy execution : vorpal .command('clean') .action(function (args,cb) { process.stdout.write ("\u001B[2J\u001B[0;0f"); cb(); });