ROADMAP: add deprecated code removal schedule

I think it's useful to have this publically available.

ROADMAP.md

@@ -7,5 +7,88 @@ functionality.
 ## Versions 0.7X.Y (as needed)
 * Neo 2.0 support (bug fixes, minor functionality additions)
 
-## Version 1.0 (2022, TBD)
-* stable version with full Neo N3 support and useful extensions
+## Version 0.100.0 (aligned with C# node 3.5.0 release, ~December 2022)
+ * 3.5.0 protocol changes
+ * drop some deprecated code (see below)
+ * RPC wrappers generator with extended type information
+
+## Version 1.0 (2023, TBD)
+ * stable version
+
+# Deprecated functionality
+
+As the node and the protocol evolve some external APIs can change. Usually we
+try keeping backwards compatibility for some time (like half a year) unless
+it's impossible to do for some reason. But eventually old
+APIs/commands/configurations will be removed and here is a list of scheduled
+breaking changes. Consider changing your code/scripts/configurations if you're
+using anything mentioned here.
+
+## getversion RPC reply Magic and StateRootInHeader fields
+
+"getversion" RPC reply format was extended to contain "protocol" section in
+version 0.97.3. Since then we have deprecated Magic and StateRootInHeader
+fields in the Version structure that allows to decode replies from pre-0.97.3
+servers while RPC server implementation populates both old and new fields for
+compatibility with pre-0.97.3 clients.
+
+Version 0.97.3 was released in October 2021 and can't really be used today on
+public networks, we expect at least 0.99.0+ to be used in production (0.99.2+
+for C# 3.4.0 compatibility). Therefore these old fields are scheduled to be
+removed in version 0.100.0 both client-side and server-side. If any of your
+code uses them, just use the Protocol section with the same data.
+
+## InitialGasDistribution field of getversion RPC reply
+
+An incompatibility with C# node's InitialGasDistribution representation was
+detected and fixed in version 0.99.0 of NeoGo (June 2022). Some compatibility
+code was added to handle pre-0.99.0 servers on the client side, however it was
+not possible to change pre-0.99.0 clients to work with newer servers.
+
+We expect all servers to be migrated to 0.99.0+ by now, therefore
+compatibility code will be removed in version 0.100.0.
+
+## Old RPC client APIs
+
+A huge set of RPC client APIs was deprecated in versions 0.99.2 and 0.99.3
+(August-September 2022), including very frequently used ones like
+SignAndPushInvocationTx, AddNetworkFee, TransferNEP17. A new set of
+invoker/actor/unwrap/nep17/etc packages was introduced decoupling these
+functions from RPC client and simplifying typical backend code. Please refer
+to rpcclient package documentation for specific replacements for each of these
+APIs and convert your code to using them.
+
+While a lot of the code is already converted to new APIs, old ones still can
+be used in some code not known to us. Therefore we will remove old APIs not
+earlier than February-March 2023, with 0.101.0 or 0.102.0 release.
+
+## util.FromAddress smart contract helper
+
+`util` smart contract library has a FromAddress function that is one of the
+oldest lines in the entire NeoGo code base, dating back to 2018. Version
+0.99.4 of NeoGo (October 2022) has introduced a new `address` package with
+`ToHash160` function, it covers a bit more use cases but can be used as a
+direct replacement of the old function, so please update your code.
+
+util.FromAddress is expected to be removed around March 2023 (~0.102.0
+release).
+
+## WSClient Notifications channel and SubscribeFor* APIs
+
+Version 0.99.5 of NeoGo introduces a new set of subscription APIs that gives
+more control to the WSClient user that can pass specific channels to be used
+for specific subscriptions now. Old APIs and generic Notifications channel are
+still available, but will be removed, so please convert your code to using new
+Receive* APIs.
+
+Removal of these APIs is scheduled for March-April 2023 (~0.102.0-0.103.0
+releases).
+
+## Prometheus RPC counters
+
+A number of neogo_${method}_called Prometheus counters are marked as
+deprecated since version 0.99.5, neogo_rpc_${method}_time histograms can be
+used instead (that also have a counter).
+
+It's not a frequently used thing and it's easy to replace it, so removal of
+old counters is scheduled for January-February 2023 (~0.100.X release).