Integrate segmentio/ware

segmentio/ware, on which metalsmith depends has been unmaintained for a long time and is only a single file of code. Except modernization, integrating the package as a metalsmith module will allow ms to customize how ware.js operates eventually (this is useful for example to formally disallow metalsmith.use'ing multiple plugins in a single invocation, which is not a common pattern and brings little added value and is confusing with the metalsmith.json format)