add jitter stat, alpha aesthetic, change entry point

what used to be C(...).render('svg')
is now C('svg').q(...).render()

This will eventually become a fully fluent api
that supports something like


C('svg', {data: data})
  .stat.jitter()
  .geom.point({ x: 'time', y: 'value' })
  .geom.smooth({ method: 'lm' })
  .render()

but .q() will be the quick entry point