maint: Add .mailmap

While browsing history, I noticed that 91a619c looked a bit awkward
compared to its successor be3370d, based on encoding choices made
differently between the two commits.  There may be other situations
where we want to use .mailmap, but this serves as a good start. You
may want to 'git config log.mailmap true' to use the mailmap by
default when browsing history.

Signed-off-by: Eric Blake <eblake@redhat.com>

Author: ebblake

.mailmap

@@ -0,0 +1,4 @@
+# This mailmap fixes up author names/addresses.
+# Search for mailmap in 'git shortlog --help' for syntax.
+
+Tuomas Jorma Juhani Räsänen <tuomasjjrasanen@tjjr.fi>