Remove echo, Create _echo Function, Use printf

According to the POSIX standard `echo` has an unspecified behavior if using `-n`

Create private function `_echo` to use printf

References:
http://pubs.opengroup.org/onlinepubs/9699919799/utilities/echo.html#tag_20_37_16
http://wiki.bash-hackers.org/scripting/nonportable#echo_command

Fixes #64