add 1.html

first jquery function
level 2 done
append, prepend, after, before, remove
3.2 Acting on Interaction
refactor using this
refactor using closest
edit README.md
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