Starting a new branch. Added protocol description

docs/sync.markdown

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+# INTRO #
+
+This document discribes the server sync protocol.
+
+# DRAFT PROTOCOL DESCRIPTION #
+
+Version:
+* Protocol version
+* Model version
+
+Node data:
+* Public key
+
+Object data:
+* Post
+* Post list (for sync)
+
+The node requests other node's changes list since some time (since epoch if
+this is the start). The other node sends a list of post ids or posts in the
+XML or JSON format.
+
+Protocol version is the version of the sync api. Model version is the version
+of data models. If at least one of them is different, the sync cannot be
+performed.
+
+The node signs the data with its key. The receiving node saves the key at the
+first sync and checks it every time. If the key has changed, the info won't be
+saved from the node (or the node id must be changed).