Should I be able to initialize a masked table by passing in a mask?

In the initial implementation it was forseen that users could initialize a table object with a mask to create a masked table from e.g. a list of lists of values and a list of lists of boolean values as a mask.

This feature made it into the docstring, but not into the code.
```
mask : numpy ndarray, dict, list, optional
   The mask to initialize the table
```
https://github.com/astropy/astropy/blob/master/astropy/table/table.py#L885

In #1187 (when changing other parts of the docstring) this was discovered and moved from the docstring into a comment in the code.

This issue is here to remind us that either am implementation of this should be added or we should have a conscious decision not not offer this functionality.