use grunt-contrib-jade
add jade task to Gruntfile

ref.
  https://github.com/gruntjs/grunt-contrib-jade
  http://jade-lang.com/
add index.jade
add "jade" task into "build" task
remove app/index.html
fix index.jade
fix link tag syntax
remove H5BP message paragraph
correct script tag

script
  hoge
  fuga

is deprecated. change it to

script.
  hoge
  fuga
Merge branch 'jade-grunt'