Add V8 releases script.

This script retrieves the history of all V8 branches and trunk revisions and their corresponding Chromium revisions.

TEST=tools/push-to-trunk/releases.py -c <chrome path> --csv test.csv

BUG=
R=jarin@chromium.org

Review URL: https://codereview.chromium.org/227583002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20629 ce2b1a6d-e550-0410-aec6-3dcde31c8c00