Add a row about Total commits/insertions/deletions for all the authors

[danilovesky]

Currently the main statistics table looks as follows:

The following historical commit information, by author, was found in the repository:

Author           Commits    Insertions      Deletions    % of changes
author 1              24           564             59            10.2
author 2              21           276             97            30.2

It would be useful to add an extra row summarising the total changes for all the authors, e.g. like this (with the whole Total row being highlighted the same way as the table header):

The following historical commit information, by author, was found in the repository:

Author           Commits    Insertions      Deletions    % of changes
author 1              24           564             59            60.2
author 2              21           276             97            38.8
Total                 45           840            147             100

Note that there is an empty row in HTML output that can hold this additional information.

[adam-waldenberg]

Thank you @danilovesky.
Will add this to the todo list.