Merge pull request #117 from vsanmaster/master

fix 18 errors of w3c validator, target blank in fork github link, scale in images helper
Add more game engines
Merge pull request #118 from ellisonleao/master

Add more game engines
Added an article "A Dive Into Plain JavaScript"
Merge pull request #119 from ryanburgess/master

Added an article "A Dive Into Plain JavaScript"
fix share buttons size and margin
fix github count button size
change helpers structure
helpers new style
Adds section links
Merge pull request #120 from leobalter/section-links

Adds section links
Updates testing tools section

- Removes FireUnit and SugarTest, they were abandoned (not updated for 4+ years)
- Fixes QUnit typo
- Fixes `behind` typo on Karma desc
- Includes Istanbul (code coverage tool)
- Includes DexterJS (test helper)
Merge pull request #121 from leobalter/testing-section

Updates testing tools section
Updating Frameworks
Merge pull request #122 from vigneshshanmugam/master

Updating Frameworks
Update core.css
Merge pull request #123 from IAMFELIPESOUZA/patch-1

Update core.css
Update description for Crafty.js
Merge pull request #124 from kevinsimper/patch-1

Update description for Crafty.js
Add You Might Not Need jQuery article