Behaviour change.
`terminatesession` returns ErrUnknownSession in case of impossibility of finding session,
previously there was no-error response with `false` result.
`traverseIterator`returns ErrUnknownSession in case of impossibility of finding session,
previously there was no-error response with default result; `traverseIterator`returns ErrUnknownIterator,
there were no such errors before.
Accordingly to proposal:
https://github.com/neo-project/proposals/pull/156
Also adding description of `traverseIterator` in docs/rpc.md.
Signed-off-by: Tatiana Nesterenko <tatiana@nspcc.io>
f3760c1a98