refactor .requires, documentation for .requires and .addComponent

Now that addComponent does not re-add components that are already added,
it has become exactly the same as requires. Therefore I deleted the
redundant code and clarified the documentation.
edit requires documentation
Update core.js

Improve the condition to triple equal.
Merge pull request #537 from matheusazzi/patch-1

Update core.js
Fixing timing test based on game loop refactor.
Merge pull request #535 from sbyrnes321/develop

refactor .requires, documentation for .requires and .addComponent
Merge pull request #538 from ericathegreat/stage-testfix

Fixing timing test based on game loop refactor.
Create .travis.yml Fixed #540
Updated package.json with the default test script
Make Color and Sprite components work together for DOM elements
Merge pull request #542 from zipang/develop

Fix: Make Color and Sprite components work together for DOM elements