grid api

do you think this is confusing? it may actually be easier for users to grok if we given them just a couple options.

`py.grid_ops.append_rows(rows, grid=grid.id)`
OR
`py.grid_ops.append_rows(rows, grid_url="https://plot.ly/~chris/3")`

We can always add them in later, but i don't like having *too* many ways to call things. Just my opinion.