So, for example, photometry, redshifts, postion queries could all have their own `_parse` methods, but there should be specific reference to these options in the docstring of `get_table`:

```
def get_table('M31',type='photometry',**kwargs):
    """
    
    Parameters
    ---------------
    table : [ 'photometry' | 'redshifts' | 'positions ]    
    error_bars : bool [optional for photometry]
    ref_extend : bool [optional for references]       
    """
```
something like that