Add tool to build an API tarball for distribution.

(imported from commit eeaf9f526f243cc628eede603fe1b1691c34977f)

api/README

@@ -0,0 +1,4 @@
+The Humbug API Python bindings require the following Python libraries:
+
+* simplejson
+* requests (version >= 0.12)

tools/build-api-tarball

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+#!/bin/sh -x
+ref="$1"
+if [ -z "$ref" ]; then
+    echo "You must specify the ref to base the API tarball on."
+    exit 1
+fi
+git archive --prefix=humbug-api/ -o /tmp/humbug-api.tar.gz "$ref" api/examples/ api/common.py api/__init__.py api/README