Updates

• Gaia Theme
  • Change themes by View -> Themes
  • Add Directives: $theme, template
    　
• Support custom scale image: ![50%](...)
• Support image centering: ![center](...)
• Implement context menu on editor (yhatt/mdslide#17)
• View menu's states store per window
• Help menu: Access sites and open examples
• Improve initializing window displayed as flashing
• Bugfix: Lose contents on PDF in using only Markdown View
• Bugfix on OSX: Window can zoom with pinch or double-tap

For Developers

• Update to Electron 1.2.2, jQuery 3.0.0
• Use npm start instead of gulp run