Implement `clear_database`, `insert_data` feature to WData python library.
Description:
Demo.py code needs to be extended by wdata.io.WData.save(res) command after res is initialized in lined 54-66. Once it does then the code executes correctly. However, if one wants to run it again we are stuck with the error that the file already exist. Thus the solution is to create a clear_database method in wdata.io that would remove all *.wdat files.
This wont cover all the possible desires of a User. Thus, I would also suggest to create insert_data method which would insert new datablock at the end of the *.wdat files.
@mforbes Do You think that it would cover all the possible interactions with the wdata?