Improved rendering of class name

The prior text, "__holmes-debug__", was rendered exactly thus.
By using `holmes-debug`, the markdown is rendered as a code section.
This helps with the confusion some might have that their class
should be __holmes-debug__.
Merge pull request #16 from awayken/patch-1

Improved rendering of class name
Merge pull request #1 from redroot/master

Improved rendering of class name