Change echo to printf for portability.

This MIGHT address bugs #5 and #8 about that "-e" flag getting printed. echo has portability issues so it's better to use printf (for instance see http://bit.ly/18IxWBY). The only difference is printf won't print a terminal newline, which shouldn't make any difference the way it's being used here.

Unfortunately all my machines either support -e, or echo implicitly supports backslash escapes, so I'm not able to replicate the original issue. However, I'm using the printf version and it hasn't changed the output at all, so there's that.