code: function generateLetterIcon(letter, cb) {
      // Derive SVG from base letter SVG
      var letterSVG = baseSVG;
      
      // Get a random Material Design color
      var color = getRandomLetterColor();
      
      // Substitude placeholders for color and letter
      letterSVG = letterSVG.replace('{c}', color);
      letterSVG = letterSVG.replace('{x}', letter);
      
      // Get filesystem-friendly file name for letter
      var fileName = getIconFilename(letter);
      
      // Define SVG/PNG output path
      var outputSVGPath = rootDir + config.dist.path + config.dist.svg.outputPath + fileName + '.svg';
      var outputPNGPath = rootDir + config.dist.path + config.dist.png.outputPath + fileName + '.png';
      
      // Export the letter as an SVG file
      fs.writeFileSync(outputSVGPath, letterSVG);
      
      // Convert the SVG file into a PNG file using svg2png
      svg2png(new Buffer(letterSVG), config.dist.png.dimensions)
      .then(function (buffer) {
          // Write to disk
          fs.writeFileSync(outputPNGPath, buffer);
  
          // Success
          cb();
      }).catch(function (err) {
          // Report error
          return cb(err);
      });
  }
docs: Generates icons for a single letter