Create a "dist" directory for releasing built files.

Files in the "dist" folder will be included with NPM packages and will be
the contents of Zip release files.

Progress on #74.
Update the README with website link and a NPM version badge.
Merge pull request #142 from nicksay/releases

Create a "dist" directory for releasing built files.
Merge pull request #143 from nicksay/docs-readme

Update the README with website link and a NPM version badge.
Update API to allow only one URL per name during script/style loading.

To maintain backwards compatibility across versions, this change only updates
the API documentation and throws a non-blocking error if an unsupported array
of URLs is passed instead of a single URL.  Afterwards, a following change can
safely transition the implementation without affecting the API.

Progress on #25.