Factor some macros out to common.h file.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>
Project rename to "ruby-fizzbuzz" from just "fizzbuzz".

This is to avoid clashes with other projects on Rubygems web site.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>
Update README and Rakefile.

Signed-off-by: Krzysztof Wilczynski <krzysztof.wilczynski@linux.com>