build+ci: switch to python3

Also in this commit:
 * Sync CI scripts with other projects
 * Sync sphinx_build waf tool with ndn-cxx
 * Modernize docs/conf.py
 * Replace redmine_issue extension with sphinx.ext.extlinks
 * Fix typo in docs/doxygen.conf.in
 * Improve README.md

Refs: #5095
Change-Id: Iee05500f907442dd7cb3e41bd613beef7461dab4
diff --git a/.mailmap b/.mailmap
new file mode 100644
index 0000000..7345b69
--- /dev/null
+++ b/.mailmap
@@ -0,0 +1 @@
+<davidepesa@gmail.com> <davide.pesavento@lip6.fr>