Twee language tools VS Code extension reads story format version from
the StoryData passage, and it does not hurt to keep it there. Also
remove the format argument from the Gulp build files, as tweego can
reads it from the StoryData object.

The build relies on case-sensitive sort when concatenating sources, but
gulp-sort uses localized compare by default, which can be
case-insensitive.

Optionally minify HTML file using the bundled minifier.

Gulp runs shell pipe for each source file, which are now 3. Redefine the
tweego task as a simple shell command to run tweego only once.

Pass correct path when writing and referencing sourcemap file to make it
work with external sourcemaps.