Allow users to pass an index_path or array of index_paths to update_table_data.

When this is passed, it won't update the entire table data, but just the cell or cells that correspond to the index_path(s) passed.

Don't merge now. Just opening for discussion. Needs tests too.
Nah, just thought it was cool! There is also `.any?` which matches if any are true, `.none?` if none are true, and `.one?` if only one is true. :-) 

http://ruby-doc.org/core-2.1.2/Enumerable.html#method-i-any-3F