fix(rpc): re-export lightningrpc::Error

In `v0.2.0` the `pub enum Error` are defined in `error.rs` file included in the `clightningrpc`, and I can import in my example by `clightningrpc::Error`.

In the following releases, the `error.rs` file is moved inside `common` subfolder, but it looks no public exposed from `clightningrpc`. A fast fix could be mark as public the following line
`pub use clightningrpc_common::errors::Error;` in `lightningrpc`. So I could import the `enum Error` in my example by `clightningrpc::lightningrpc::Error`.

Suggested-by: @lvaccaro <me@lvaccaro.com>
Signed-off-by: Vincenzo Palazzo <vincenzopalazzodev@gmail.com>

rpc/src/lib.rs

@@ -38,3 +38,4 @@ pub mod types;
 
 // Re-export high-level connection type
 pub use crate::lightningrpc::LightningRPC;
+pub use clightningrpc_common::errors::Error;