Feature Request: regex for drop
Don't have time to implement this, but I wanted to float the idea and park it. It's pretty trivial and you can achieve the same thing with filter, but it might be nice if drop had a regex keyword. E.g., these would be equivalent

```
df = df.filter(regex="^(?!var_start)")
df = df.drop(regex="^var_start", axis=1)
```
