Code for how to create a ring buffer without C++ Standard Template Library.

This code accompanies the article "Ring buffer basics" by Ken Wada, July 2013, Embedded.com.
The ring buffer's first-in first-out data structure is useful tool for transmitting data between asynchronous processes.
The article shows how to bit bang one in C without C++'s Standard Template Library.

Signed-off-by: cctsao1008 <chiacheng.tsao@gmail.com>