IE 11 support

Added un-prefixed touch-action CSS attribute
added un-prefixed PointerEvents event handler hooks
IE11 Support

Added unprefixed touch-action CSS attribute
Added unprefixed pointer events handlers hooks
windows.navigator.pointerEnabled

for backward compatibility reasons, IE11 sets both msPointerEnabled and
pointerEnabled. Changed the order for the test and added 'else if' to
not duplicate handlers on pointer events
add example for parallax backgrounds
Merge branch 'dev' of github.com:hakimel/reveal.js
Merge branch 'dev' of github.com:hakimel/reveal.js
First refactoring
Remove section attribute implementation.
Fix element attributes, except for multi-line.
Fix previous element selection.
Removes console.log calls.
Simpler default syntax for markdown attributes.

- on slides: .slide x=y
- on elements: .element x=y

Those are detected in html comment, in order to not be visible
if a markdown is edited in an html editor.
test-markdown-attributes.*, new default separator

- Reformat.
- Change default separator test 'slide: x=y'
test-markdown-element-attributes: formats and test.

- Reformat
- Use new default separator format: '.element: x=y'
- Add new tests for testing that default format
README.md mentions the new default separators.

- new default separator for slide attributes
- new default separator for element attributes
Illustrate both, in html comments.
Merge branch 'attributes' of https://github.com/VonC/reveal.js into dev
readme correction for #734
add example of markdown slide and element attributes
rename markdown attribute test files to same format
2.6.1 #734