Move download.sh script to tools tree

tools/download.sh

@@ -0,0 +1,50 @@
+#!/usr/bin/env bash
+
+[[ -n $GITHUB_TOKEN ]] || { echo >&2 "GITHUB_TOKEN variable is undefined, please provide token"; exit 1; }
+
+# Authorizes with read-only access to GitHub API
+curl_() {
+    curl -s -i -H "Authorization: token $GITHUB_TOKEN" "$@"
+}
+
+# Retrieves asset ID and package name of asset ending in argument
+# $info looks like: "id": 1698239, "name": "powershell_0.4.0-1_amd64.deb",
+get_info() {
+    curl_ https://api.github.com/repos/PowerShell/PowerShell/releases/latest | grep -B 1 "name.*$1"
+}
+
+# Get OS specific asset ID and package name
+case "$OSTYPE" in
+    linux*)
+        # Install curl and wget to download package
+        sudo apt-get install -y curl wget
+        info=$(get_info deb)
+        ;;
+    darwin*)
+        info=$(get_info pkg)
+        ;;
+    *)
+        exit 2 >&2 "$OSTYPE not supported!"
+        ;;
+esac
+
+# Parses $info for asset ID and package name
+read asset package <<< $(echo $info | sed 's/[,"]//g' | awk '{ print $2; print $4 }')
+
+# Downloads asset to file
+curl_ -H 'Accept: application/octet-stream' https://api.github.com/repos/PowerShell/PowerShell/releases/assets/$asset |
+    grep location | sed 's/location: //g' | wget -i - -O $package
+
+# Installs PowerShell package
+case "$OSTYPE" in
+    linux*)
+        # Install dependencies
+        sudo apt-get install -y libunwind8 libicu52
+        sudo dpkg -i ./$package
+        ;;
+    darwin*)
+        sudo installer -pkg ./$package -target /
+        ;;
+esac
+
+echo "Congratulations! PowerShell is now installed."