sausage-plugin part 1: run, #[rpc], #[schema], rpc.discover, calls, locks, Ctx, hooks

Checkpoint. Known issues, fixed in part 2: short writes on stdout,
byte-wise stdin reads, Result suffix on all result schemas, lost enum
variant docs, serde errors as invalid params, missing item docs.

sdk/Cargo.toml

@@ -6,3 +6,14 @@ description = "SDK for Sausage plugins."
 
 [dependencies]
 sausage-plugin-macros = { version = "0.1", path = "macros" }
+sausage-interface = { path = "../interface" }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+schemars = "1"
+futures = "0.3"
+
+[target.'cfg(target_os = "wasi")'.dependencies]
+wstd = "0.6"
+
+[dev-dependencies]
+trybuild = "1"