Deprecated messages should result in their en/decoders marked with @Deprecated

[ratcashdev]

given a definition like

<sbe:message name="MyDeprecatedMessage" id="123"
    description="old message that was deprecated in version 45" deprecated="45">

its respective java encoder and decoder should be marked with the @Deprecated annotation so that users get compile time warnings when still using old messages.

Happy to submit a PR, if this issue and objectives are accepted.

[mjpt777]

I'd be happy to review an PR on this.