Release 1.3.0

Updates

• New homepage layout and image (#255).
• Accessibility linting via aXe (#344).
• Fix relative links in external markdown files (#324).
• Improve documentation around how the site fetches dynamic content.
• Bump USWDS version to 1.3.0.

New Content

• Added Form validation documentation (#338).
• New case study for Vets.gov (#347)