Add main to package.json

In order to require() and use Leaflet via browserify requires
that the package define a main entry point for the module.
Merge pull request #1476 from jwalgran/master

Add main to package.json
Fix zooming on browsers without zoom animation support. Refs #1486
Merge pull request #1487 from danzel/zoom-fixes

Fix zooming on browsers without zoom animation support. Refs #1486
Fix opacity in oldie for the millionth time. Refs #1486
Merge pull request #1490 from danzel/oldie-fixes

Fix opacity in oldie for the millionth time. Refs #1486
Disable 3D CSS transforms on PhantomJS

PhantomJS does not support 3D CSS transform even though it's a Webkit product. This patch detects PhantomJS in the user agent and disables 3D transforms.

Details on PhantomJS support are here: https://groups.google.com/forum/#!msg/phantomjs/h7-4-CWsy1g/KX1tlf5gT5IJ
Merge pull request #1501 from rassie/patch-1

Disable 3D CSS transforms on PhantomJS
fix jshint 1.1.0 errors, update deps and build