use data tag
remove duplication

extract variable
specify exact button

there're 2 solutions.
add/remove highlight effect using filter/addClass/removeClass
Merge branch 'feature/traversing-and-filtering' into develop

* feature/traversing-and-filtering:
  add/remove highlight effect using filter/addClass/removeClass
  specify exact button
  remove duplication
  use data tag
add slidDown effect
add mouseenter event handling
remove duplication
add keyup event handling
modify README.md
add click event handler

- use fadeToggle
preventDefault

- in order to prevent page reloaded
Merge branch 'feature/on-dom-load' into develop

* feature/on-dom-load:
  preventDefault
  add click event handler
  modify README.md
  add keyup event handling
  remove duplication
  add mouseenter event handling
  add slidDown effect
change css when clicked
refactoring
show price class
little change
add animation
Merge branch 'feature/taming-css' into develop

* feature/taming-css:
  add animation
  little change
  show price class
  refactoring
  change css when clicked