Update tally

This pull requests finally puts tally objects as load-able and save-able objects to and from hdf5, similar to the existing material object capability. All comments welcome!
Also, for HDF5, the column & dataset names should be words in most programming languages. That is, they should match the regex `[A-Za-z_][0-9A-Za-z_]*`. Notably there should not be any spaces and preferable they would follow the `function_name_convention`.  Column names as words enables some nice features upstream such as tab-completion in interactive environments.