docs: auto generate backend options documentation

This inserts the output of "rclone help backend xxx" into the help
pages for each backend.

bin/make_backend_docs.py

@@ -0,0 +1,67 @@
+#!/usr/bin/env python
+"""
+Make backend documentation
+"""
+
+import os
+import subprocess
+
+marker = "<!--- autogenerated options"
+start = marker + " start"
+stop = marker + " stop"
+
+# directory name to backend name
+dir_to_backend = {
+    "googlecloudstorage": "google cloud storage",
+    "amazonclouddrive": "amazon cloud drive",
+}
+
+def find_backends():
+    """Return a list of all backends"""
+    return [ x for x in os.listdir("backend") if x not in ("all",) ]
+
+def output_docs(backend, out):
+    """Output documentation for backend options to out"""
+    backend = dir_to_backend.get(backend, backend)
+    out.flush()
+    subprocess.check_call(["rclone", "help", "backend", backend], stdout=out)
+
+def alter_doc(backend):
+    """Alter the documentation for backend"""
+    doc_file = "docs/content/"+backend+".md"
+    if not os.path.exists(doc_file):
+        raise ValueError("Didn't find doc file %s" % (doc_file,))
+    new_file = doc_file+"~new~"
+    altered = False
+    with open(doc_file, "r") as in_file, open(new_file, "w") as out_file:
+        in_docs = False
+        for line in in_file:
+            if not in_docs:
+                if start in line:
+                    in_docs = True
+                    start_full = start + " - DO NOT EDIT, instead edit fs.RegInfo in backend/%s/%s.go then run make backenddocs -->\n" % (backend, backend)
+                    out_file.write(start_full)
+                    output_docs(backend, out_file)
+                    out_file.write(stop+" -->\n")
+                    altered = True
+            if not in_docs:
+                out_file.write(line)
+            if in_docs:
+                if stop in line:
+                    in_docs = False
+    os.rename(doc_file, doc_file+"~")
+    os.rename(new_file, doc_file)
+    if not altered:
+        raise ValueError("Didn't find '%s' markers for in %s" % (start, doc_file))
+
+if __name__ == "__main__":
+    failed, success = 0, 0
+    for backend in find_backends():
+        try:
+            alter_doc(backend)
+        except Exception, e:
+            print "Failed adding docs for %s backend: %s" % (backend, e)
+            failed += 1
+        else:
+            success += 1
+    print "Added docs for %d backends with %d failures" % (success, failed)