URL support fot get_embed()

I added URL support for plotly.tools.get_embed() and plotly.tools.embed()
so that

plotly.tools.get_embed('https://plot.ly/~etpinard/270/')

and

plotly.tools.get_embed('etpinard','270')

are both accepted just like in plotly.plotly.get_figure().

I also corrected a few typos in docstring for plotly.plotly.get_figure()