add mailmap

[umarcor]

This PR adds a .mailmap file for cleaning the output of git's author list, which is used in tools such as gource or gitinspector.

Without this PR:

# git shortlog --summary --numbered --email
  1735  stnolting <stnolting@gmail.com>
   180  Stephan <stnolting@gmail.com>
    86  umarcor <unai.martinezcorral@ehu.eus>
     7  Lars Asplund <lars.anders.asplund@gmail.com>
     4  tmeissner <programming@goodcleanfun.de>
     3  AWenzel83 <Andreas.Wenzel@hs-wismar.de>
     2  Andreas Wenzel <Andreas.Wenzel@hs-wismar.de>
     1  Pascal Cotret <pascal.cotret@gmail.com>
     1  Unai Martinez-Corral <38422348+umarcor@users.noreply.github.com>

With this PR:

# git shortlog --summary --numbered --email
  1915  Stephan Nolting <stnolting@gmail.com>
    88  Unai Martinez-Corral <unai.martinezcorral@ehu.eus>
     7  Lars Asplund <lars.anders.asplund@gmail.com>
     5  Andreas Wenzel <Andreas.Wenzel@hs-wismar.de>
     4  Torsten Meissner <programming@goodcleanfun.de>
     1  Pascal Cotret <pascal.cotret@gmail.com>

[stnolting]

I just googled the purpose of a .mailmap file - I was not aware of it (or the "issue" it closes) at all 😅
This file needs to be updated manually if there are new contributors, right?

[umarcor]

I just googled the purpose of a .mailmap file - I was not aware of it (or the "issue" it closes) at all 😅
This file needs to be updated manually if there are new contributors, right?

Yes, and no. You can update it if you want, but it will not "hide" the contributors which are not listed in the mailmap. It is just a table of aliases/replacements which is used if any of those show up. For instance, if I remove Stephan Nolting <stnolting@gmail.com> <stnolting@gmail.com> from the mailmap I get:

# git shortlog --summary --numbered --email
  1735  stnolting <stnolting@gmail.com>
   180  Stephan <stnolting@gmail.com>
    88  Unai Martinez-Corral <unai.martinezcorral@ehu.eus>
     7  Lars Asplund <lars.anders.asplund@gmail.com>
     5  Andreas Wenzel <Andreas.Wenzel@hs-wismar.de>
     4  Torsten Meissner <programming@goodcleanfun.de>
     1  Pascal Cotret <pascal.cotret@gmail.com>

As you see, the results from Stephan/stnolting were not hidden, but it does not know that those are the same person.

Therefore, you don't need to update the mailmap when new contributors arrive; you can do it if you want when some existing contributor uses a new e-mail name.

[stnolting]

Now I get it 😄
Thank you 👍