Roadmap to 1.0.0

[mrmlnc]

• [x] Use @types, update dependencies and target plugin only for VS Code 1.8.0 and above
• [ ] Code refactoring
  • [ ] Move common code to vscode-css-intellisense
  • [ ] Use classes for parser, providers and services
  • [ ] Simplify Completion and SignatureHelp provider
  • [ ] Scanner optimization (if it's possible)
  • [ ] Cache -> Storage
• [ ] Remove autocomplete for Variables and Mixins inside current document (covered by VS Code, fix #27)
• [ ] Fix problem with update cache from current document
• [ ] Add support for @a : 1;
• [ ] Remove preview status
• [ ] May be add support foe "Find All References to a Symbol" (#30)