ENH: add regex to pandas.DataFrame.isin function (possible speed up?)
I think it would be nice if regex were compatible with `pandas.DataFrame.isin`. 

Lets say I am inputting the way snakes attack in a dataframe df I would tagging a column `df['Attack method']` using a list `poison` and a list `squeeze` to check if there are matches in `df[Genus]`

```
df['Attack method'] = (df.Genus.isin(poison).map({True:'Poison',False:''}) +
                df.Genus.isin(squeeze).map({True:'Squeeze',False:''}))
```

If I was using Regex I would have to somehow get rid of the user warning

```
UserWarning: This pattern has match groups. To actually get the groups, use str.extract.  " groups, use str.extract.", UserWarning
```

and create for loops like this:

```
for i in range(len(poison)):
    df.loc[df.Genus.str.contains(poison[i]) & (df.Attack method == ''),'Attack method'] = 'Poison'
for i in range(len(squeeze)):
    df.loc[df.Genus.str.contains(squeeze[i]) & (df.Attack method == ''),'Attack method'] = 'Squeeze'
```

unless there are other ways I missed out?
