v1.0.3: Accessibility improvements and keyboard navigation

• jQuery dependency updated, <3.0 has XSS vulnerabilities
• Demo file included for integration testing
• Accessibility improvements
• Use instead of to ensure focus from keyboard navigation.
• Improve z-index to ensure focus ring is not hidden behind other elements.
• Maintain focus after selecting an item from dropdown.
• Use aria-haspopup='listbox' for dropdown and remove conflicting tags from options.
• Use aria-hidden and aria-expanded to notify browser of widget state.
• Handle keyboard navigation between options when listbox is expanded.