Path to Shiba 1.0

• watcher refactorings; Send only path to renderer process from main process. Currently whole text is sent to renderer process but ipc of Electron is not fast. Converting markdown document to HTML will be performed in renderer process asynchronously.
• Add gantt charts support for mermaid.js
• Task list
• Search in page feature using found-in-page event
• Replace 'open in external' hack with marked renderer customization
• Fix the menu panel on scrolling the preview area.
• Move menu panel to the left and enable to hide title bar
• Detect Electron version
• Enable to specify code block theme
• Enable to specify Markdown CSS (default: github-markdown-css)
• File update notification using HTML5 notification API
• Font size configuration
• Add tooltip to markdown links
• Table of Contents
• Rotate 'reload' icon on update
• Optimize start loading time (especially mermaid.min.js looks slow)