This allows plugins to choose how to present things in getmanifest.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Changelog-Added: plugins: `getmanifest` may now include "allow-deprecated-apis" boolean flag.
Changelog-Deprecated: plugins: `getmanifest` without any parameters; plugins should accept any parameters for future use.
Rusty Russell