Add logic to push benchmark json to github to archive (#110)
Store data in either 'master' or 'pull_request' subdir of 'project/repo'
top level dir. Maintain 'latest' symlink for master data only.
Currently, master sytest mlink is updated on every run, since PR jobs
are expected to gate regressions. However, we could change this and
follow a different protocol for when, and how often, to move the
pointer.
