Implement pandas like rename

[janakact]

Intended to fix #80

[maartenbreddels]

Hi,

thanks for your first-time contribution! I like the idea of this, but I'm not sure of the method name. @JovanVeljanoski what do you think. Should we mayne rename the existing rename, or have 1 rename method that takes a dict or two arguments?

Regards,

Maarten

[janakact]

Hi @maartenbreddels, Thank you for this marvelous library.
Yeah. Of course name should be changed I think, it should be similar to pandas I guess. May I add an if condition to check whether the input is a dict to support both vaex and pandas API?

[JovanVeljanoski]

I wonder if the current rename and pandas_rename can be refactored to be a single function.

For example, if the name argument is collections.Mapping instance, than do what pandas_mapping does, otherwise assume the current rename method's functionality.

Also, would be nice if this branch were rebased on master, lots of changes in the meantime, would help with the CI.

[JovanVeljanoski]

Is there a reason to do df = self.copy() instead of just doing the rename on self directly (like the existing rename method is doing? (Maybe @maartenbreddels knows).