refactor bootstrap

.config/yadm/bootstrap

@@ -6,6 +6,19 @@
 
 set -eu
 
+# Download file and return filename
+function download () {
+    [[ $# == 0 ]] && exit 1
+
+    local url="$1"
+    local suffix="${2:-"${url##*.}"}"
+    local filename="$(mktemp -t "download-XXXXXX.${suffix}")"
+
+    curl --location --output "${filename}" -# "${url}"
+
+    echo "${filename}"
+}
+
 # Directory to look for bootstrap executables in
 BOOTSTRAP_D="${BASH_SOURCE[0]}.d"