Add vaex.import as a dispatcher to vaex.from_*

[datascienceit]

instead of

vx.from_pandas .
vx.from_ascii .
vx.from_arrays .
vx.from_astropy_table .

Just have vx.read()/ vx.import()/ vx.create() and deal with it in the read function.

[maartenbreddels]

well, vaex.open(...) understands cvs now. See the docstring. I think chaning the API at this time for this is not worth it.

[maartenbreddels]

I like the import idea btw, keeping this open.