Add Replace method.

[alexpantyukhin]

Would be a good to add the replace method from the pandas? Actually there is already method Merge exists which could be used for replaceing functionality, but I think Replace would be more clear. Any thoughts?

[sebhofer]

I'm generally in favour of adding more "convenience" functions to Deedle.

@zyzhu I myself have a list of function which I would like to have in Deedle (e.g., basic list operations such as exists, choose etc.). Do you find it useful if we just go ahead and start implementing such functionality?

[zyzhu]

Please go ahead. The rule of thumb is to match the convenience functions with pandas. It will increase the user experience of using Deedle. Please send the pull requests whenever you are ready and we can keep discussing it in the pull. Just like what we did on describe function.

We will also need to work on documentation and sample notebooks in the future to prove the points.