Adds a .mailmap file to fix names & emails in git shortlog (#1476)

As reported in #1472, a number of people have committed under multiple
names/email addresses. This splits their contributions as reported by 'git
shortlog'.

The .mailmap file fixes the issue as can be checked by running
`git shortlog -sn | wc -l` which should return the current number of
contributors, i.e. 105.

It also allows people to change the formatting of their name, if desired,
in the shortlog stats.

.mailmap

@@ -0,0 +1,14 @@
+# If you have a preferred format for your name to be listed in git shortlog,
+# add it here.
+# The format can be found here: https://git-scm.com/docs/git-shortlog
+
+emilkris33 <[email protected]> Emil <[email protected]>
+
+Koosemose <[email protected]> koosemose <[email protected]>
+
+Martin "quill18" Glaude <[email protected]> Martin "quill18" Glaude <[email protected]>
+Martin "quill18" Glaude <[email protected]> Martin 'quill18' Glaude <[email protected]>
+
+relinu <[email protected]> Chris <[email protected]>
+
+sboigelot <[email protected]> Togis <[email protected]>