Fix build against libv8 3.24.5
Make compatible with V8 3.23.11 (and below)
Make compatible with V8 3.23.8 (and below)
Make compatible with V8 3.23.2 (and below)
Update README, removed build badge, require V8 3.22.3

GitHub now caches the build badge image if it is served via HTTP.
However the Jenkins box has no SSL certificate, hence I had to remove
the badge.
Merge pull request #82 from stesie/fix-ftbfs-v8-3.24.5

Fix build against V8 >= 3.24.4