Handle two horizontal rules abutting a paragraph.

Closes #106.
Add JSHint support.

Use `npm run check` or `npm run lint`.
Fix many JSHint warnings.
JSHint: Enable curly rule.
Get rid of node.js v0.9 from travis; it was buggy and not stable.
package.json: Specify the minimum node.js version.
Explicitly specify the npm package contents.
GitHub is using https links, so use that.