Add slides.markdown file
Modify index.html to use slides.markdown

From now on, the slides needs to be run from a server.
Implement: toggle tile view when pressing 'T' key
Add tile-view.css file
Add tile view header
Add tile view header style
Bind click on slide to play from this slide
Add scroll to tile view

The problem is that the scroll is enabled, but the scrollbar won't show
up.
Round tile container width and height
Add div.tile to style a slide tile outline
Mark current displaying slide in tile view
Mark displayed tiles
Style tile view
Scroll the current tile into view
Add tile view mode code to script.js

Prepare to merge into master.
Add tile view mode styles in style.css

Prepare to merge into master.
Remove reference to tile-view.{js,css}
Update README.md to show tile view mode feature
Implement tile view mode

Tile view mode shows all slides of a slide show. Click on a slide, the
slide show will go on from that slide. Use keyboard 'T' to toggle
between tile view mode and play mode.

Merge branch 'tile-view'

* tile-view:
  Update README.md to show tile view mode feature
  Remove reference to tile-view.{js,css}
  Add tile view mode styles in style.css
  Add tile view mode code to script.js
  Scroll the current tile into view
  Style tile view
  Mark displayed tiles
  Mark current displaying slide in tile view
  Add div.tile to style a slide tile outline
  Round tile container width and height
  Add scroll to tile view
  Bind click on slide to play from this slide
  Add tile view header style
  Add tile view header
  Add tile-view.css file
  Implement: toggle tile view when pressing 'T' key
  Modify index.html to use slides.markdown
  Add slides.markdown file
Fix typo in tile-view.js and script.js

This typo causes the previous displayed-tile class not being removed.