Updated WebP with partial support information

Some of the browsers that support lossy Webp images, do not support lossless and alpha versions of Webp.

Google has updated their Webp page with infromation about the browser support:
https://developers.google.com/speed/webp/faq#which_web_browsers_natively_support_webp

However, the browser support that they list is not completely accurate (I think). Lossy support has probably been in Chrome before version 17. This article says that it was officially introduced in Chrome 12: http://arstechnica.com/information-technology/2011/05/mozilla-rejects-webp-image-format-google-adds-it-to-picasa/

Alpha and lossless support looks more correct (at least for Android: lossless and alpha are not supported in < 4.2), and support was indeed added with libwebp 0.2.0/0.1.99:
http://git.chromium.org/gitweb/?p=webm/libwebp.git;a=blob_plain;f=NEWS;hb=refs/heads/0.3.0

I've updated all browser versions that have only lossy support as only partially supporting Webp.