docs: function findup(dirpath, filename) {
              // Nodejs libs.
              var path = require('path');
              var fs = require('fs');
              // In Nodejs 0.8.0, existsSync moved from path -> fs.
              var existsSync = fs.existsSync || path.existsSync;
  
              var filepath = path.join(dirpath, filename);
              // Return file if found.
              if (existsSync(filepath)) { return filepath; }
              // If parentpath is the same as dirpath, we can't go any higher.
              var parentpath = path.resolve(dirpath, '..');
              return parentpath === dirpath ? null : findup(parentpath, filename);
          }