support for responder params, vdirs; bump version

Let's say you have a an app hosted at /foo/bar/baz. You probably want
servme to respond to requests for static assets that live at
/foo/bar/assets/whatever, but in the filesystem those assets live in
dist/assets, not /foo/bar/baz/dist/assets.

Configuring this vdir option makes servme do the right thing.