Take off the ruby wrapping of 'github-markdown'

[hupili]

Note evermd can interwork with any Markdown backend. One only needs to change my $_exe_markdown = line of evermd.pl.

In the survey process, I found not all the backend is satisfying. In the end, I choose "github-markdown" (in the "third" directory). However, The C library is wrapped by ruby. This introduces some other difficulties in porting evermd to all system. e.g. some system does not have ruby headers for compilation. If you look into the ruby script, you find it is a straight proxy of C library. We want to take off the ruby coat so that it is easier to port.