CI: Maintenance

- Rename .travis dir to .ci, since it isn't just for Travis
- Convert Linux build scripts to posix sh
- Clean up some scripts per shellcheck

.ci/export-azure-vars.sh

@@ -0,0 +1,13 @@
+#!/bin/sh -e
+
+# Export variables for later stages of the Azure pipeline
+# Values done in this manner will appear as environment variables
+# in later stages.
+
+# From pure-sh-bible
+# Setting 'IFS' tells 'read' where to split the string.
+while IFS='=' read -r key val; do
+    # Skip over lines containing comments.
+    [ "${key##\#*}" ] || continue
+    echo "##vso[task.setvariable variable=$key]$val"
+done < ".ci/azure-vars.env"