v1.0.0

Project maintenance taken over by Flow XO. Fixed issue with Invoice lines. Created invoice.lines.add function. Added support for node v4. Updated libxmljs to 0.14.3. Bumped the version to 1.0.0.

Note: this is a backwards-compatible release. If you were previously using v0.2.1, you should be safe to upgrade to v1.0.0.