Added alias feature

Adds an alias feature:

```javascript
program
  .command('remove <target>')
  .alias('rm')
  .description('Remove target <target>')
  .action(function() {
    /* Take action */
  });
```

Also cleans up commandHelp a little. At least for me, it never looks pretty because

```
command [options] <arg>
```

is almost always longer than the given 22 space padding, so each command lines up differently. Plus, with adding an alias, it gets even longer. This just breaks the description onto a separate line, with a bit of padding at the front (and adds a newline after each command).