Files and links contain -- for namespace::class

[tyler-gilbert]

This naming has caused some problems for me.

Could it be namespace-class.md rather than namespace--class.md.

The fix can be in helper compoundPath:

 var name = compound.name.replace(/\:/g, '-'); //namepace::api -> namespace--api
      name = name.replace('--', '-'); //namespace--api -> namespace-api
      return util.format(options.output, name);

https://github.com/tyler-gilbert/moxygen/blob/master/src/helpers.js