build+ci: switch to python3

Also in this commit:
 * Sync CI scripts with other projects
 * Modernize docs/conf.py
 * Replace redmine_issue extension with sphinx.ext.extlinks
 * Minor updates to docs/doxygen.conf.in
 * Cleanup README.md and INSTALL.rst

Refs: #5095
Change-Id: I614e876e6aed73659f4f4cea01813f4604599263
diff --git a/.jenkins.d/10-build.sh b/.jenkins.d/10-build.sh
index 6faaf55..2a60f0d 100755
--- a/.jenkins.d/10-build.sh
+++ b/.jenkins.d/10-build.sh
@@ -1,45 +1,37 @@
 #!/usr/bin/env bash
-set -e
+set -ex
 
-JDIR=$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )
-source "$JDIR"/util.sh
-
-set -x
-
-git submodule init
 git submodule sync
-git submodule update
+git submodule update --init
 
-if [[ $JOB_NAME == *"code-coverage" ]]; then
-    COVERAGE="--with-coverage"
-elif [[ -z $DISABLE_ASAN ]]; then
+if [[ -z $DISABLE_ASAN ]]; then
     ASAN="--with-sanitizer=address"
 fi
-
-# Cleanup
-sudo_preserve_env PATH -- ./waf --color=yes distclean
-
-if [[ $JOB_NAME != *"code-coverage" && $JOB_NAME != *"limited-build" ]]; then
-  # Configure/build in optimized mode with tests
-  ./waf --color=yes configure --with-tests
-  ./waf --color=yes build -j${WAF_JOBS:-1}
-
-  # Cleanup
-  sudo_preserve_env PATH -- ./waf --color=yes distclean
-
-  # Configure/build in optimized mode without tests
-  ./waf --color=yes configure
-  ./waf --color=yes build -j${WAF_JOBS:-1}
-
-  # Cleanup
-  sudo_preserve_env PATH -- ./waf --color=yes distclean
+if [[ $JOB_NAME == *"code-coverage" ]]; then
+    COVERAGE="--with-coverage"
 fi
 
-# Configure/build in debug mode with tests
-./waf --color=yes configure --debug --with-tests $ASAN $COVERAGE
-./waf --color=yes build -j${WAF_JOBS:-1}
+if [[ $JOB_NAME != *"code-coverage" && $JOB_NAME != *"limited-build" ]]; then
+    # Build in release mode with tests
+    ./waf --color=yes configure --with-tests
+    ./waf --color=yes build -j$WAF_JOBS
 
-# (tests will be run against debug version)
+    # Cleanup
+    ./waf --color=yes distclean
+
+    # Build in release mode without tests
+    ./waf --color=yes configure
+    ./waf --color=yes build -j$WAF_JOBS
+
+    # Cleanup
+    ./waf --color=yes distclean
+fi
+
+# Build in debug mode with tests
+./waf --color=yes configure --debug --with-tests $ASAN $COVERAGE
+./waf --color=yes build -j$WAF_JOBS
+
+# (tests will be run against the debug version)
 
 # Install
 sudo_preserve_env PATH -- ./waf --color=yes install