ci: Switch from Travis to AppVeyor

Since June 15th, 2021, the building on travis-ci.org is ceased. Hence switch
to AppVeyor.

ci/install.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+case "$(uname)" in
+    Linux)
+	packages=(
+	    libcunit1-dev
+	    libgcrypt20-dev
+	    librdmacm-dev
+	    xsltproc
+	)
+	for p in "${packages[@]}"; do
+	    sudo sh -c "apt-get install -y $p"
+	done
+	;;
+    Darwin)
+	;;
+esac