Option for making pandas dataframe completely immutable
It seems currently there is no option similar to numpy's [setflags](https://docs.scipy.org/doc/numpy/reference/generated/numpy.matrix.setflags.html) to make pandas dataframe completely immutable (writeable=false). We are considering a design where we use immutability to know that we can cache objects. While we can still design a system like that, it would be great if we could enforce immutability to catch any errors.