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/tests/ui/params.stderr

@@ -0,0 +1,34 @@
+error[E0277]: RPC params must be a #[schema] struct with named fields
+ --> tests/ui/params.rs:6:25
+  |
+6 |     fn bad(&self, value:String)->sausage_plugin::Result<String> {Ok(value)}
+  |                         ^^^^^^ the trait `Params` is not implemented for `std::string::String`
+  |
+help: the trait `Params` is implemented for `sausage_plugin::Empty`
+ --> src/lib.rs
+  |
+  | impl Params for Empty {}
+  | ^^^^^^^^^^^^^^^^^^^^^
+note: required by a bound in `method`
+ --> src/lib.rs
+  |
+  | pub fn method<P: Params, R: SchemaType>(doc: &mut Value, name: &str, docs: &str) {
+  |                  ^^^^^^ required by this bound in `method`
+
+error[E0277]: RPC params must be a #[schema] struct with named fields
+ --> tests/ui/params.rs:6:25
+  |
+6 |     fn bad(&self, value:String)->sausage_plugin::Result<String> {Ok(value)}
+  |                         ^^^^^^ the trait `Params` is not implemented for `std::string::String`
+  |
+help: the trait `Params` is implemented for `sausage_plugin::Empty`
+ --> src/lib.rs
+  |
+  | impl Params for Empty {}
+  | ^^^^^^^^^^^^^^^^^^^^^
+note: required by a bound in `params_type`
+ --> tests/ui/params.rs:3:1
+  |
+3 | #[sausage_plugin::rpc]
+  | ^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `params_type`
+  = note: this error originates in the attribute macro `sausage_plugin::rpc` (in Nightly builds, run with -Z macro-backtrace for more info)