This patch modernizes the 'Block::Session::info' interface. Instead of
using out parameters, the 'init' RPC function returns a compound 'Info'
object now. The rather complicated 'Operations' struct is replaced by
a 'writeable' attribute in the 'Info' object.
Fixes#3275
The 'tx_cap' RPC function is only used at session-creation time. For
this reason, it was not listed in the "official" RPC interface in
'block_session.h'. However, this makes the interface more obscure than
it needs to be. So this patch promotes it to a regular RPC function.
Issue #3092
This patch changes the top-level directory layout as a preparatory
step for improving the tools for managing 3rd-party source codes.
The rationale is described in the issue referenced below.
Issue #1082