build+ci: switch to python3

Also in this commit:
 * Sync CI scripts with other projects
 * Modernize docs/conf.py
 * Cleanup README.md
 * Use the official markdown version of the GPLv3

Refs: #5095
Change-Id: Ie607fcde1f6e41fa5efbbb41b21cb08583017442
diff --git a/.gitignore b/.gitignore
index f34d89d..608c272 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,4 +26,4 @@
 *.py[cod]
 
 # Other
-/VERSION
\ No newline at end of file
+/VERSION