build+ci: switch to python3

Also in this commit:
 * Sync CI scripts with other projects
 * Modernize docs/conf.py
 * Fix typo in docs/doxygen.conf.in
 * Cleanup README.md

Refs: #5095
Change-Id: If95b6f00e4f48a102054b47e14e9c021da069e71
diff --git a/.gitignore b/.gitignore
index e75e96c..b1d7223 100644
--- a/.gitignore
+++ b/.gitignore
@@ -29,4 +29,4 @@
 *.py[cod]
 
 # Other
-/VERSION
\ No newline at end of file
+/VERSION