Pass Vinyl file object to the function 'to(iconFile)' in a new major version

[pzhlkj6612]

Hi, this plugin is great. After sprity/sprity is no longer maintained, gulp.spritesmith-multi keeps our work going. Thank you!

Summary

• Merged Fix options function description #8.
• Limited the version of Node.js in CI.
• (Breaking change) Pass Vinyl file object to to(iconFile) in version 4.0.0.
• Added doc and a test about split sprites generation.

Changes about to(iconFile)

For now, when to(iconFile) is a function, it will receive a Vinyl file object instead of a file path string. It allows users to obtain more useful information about the file (listed in Vinyl | gulp.js § Instance properties), such as parsing the relative path of a file based on the glob path passed to gulp.src().

Since the parameter passed to to(iconFile) has been changed, some old code related to it will be broken, so I marked it as a "breaking change". According to About semantic versioning | npm Docs § Incrementing semantic versions in published packages, when backward compatibility breaks, a new major version needs to be released.

Why I change the plugin itself

I really know that the split sprites generation can be done by another way without modifying the plugin:

gulp.task('split_by_myself', ['clean'], function () {
  var opts = {
    to: function (file) {
      return path.dirname(path.relative('split/', file))
          .replace(/[\/\\ ]/g, '-')
    },
  }
  return gulp.src('split/**/*.png')
    .pipe(spritesmith(opts))
    .pipe(gulp.dest('build'))
})

In the above code, I specified the path twice, because as far as I know, the glob path is difficult to compare with any ordinary path (without asterisk). After viewing the code from lib/tile.js#L18-L26 in sprity/sprity, I think using the APIs of Vinyl file object is a better way.