feature: echo -n

[nfischer]

Add support for the -n option for the echo command. This removes the default trailing newline.

Ex.

$ echo foo bar # notice the extra space after "foo bar"
foo bar

$ echo -n foo bar # notice no extra space after "foo bar"
foo bar
$

This can be implemented using process.stdout.write() fairly easily, just remember to concatenate all arguments into a single string to pass to process.stdout.write()

[nfischer]

Fixed in #590