Plugins signature load (#349)

* saving signatures to file

* loading plugin signature from file

* is_plugin column for help command

crates/nu-command/src/core_commands/help.rs

@@ -114,6 +114,12 @@ fn help(
                     span: head,
                 });
 
+                cols.push("is_plugin".into());
+                vals.push(Value::Bool {
+                    val: cmd.2,
+                    span: head,
+                });
+
                 cols.push("usage".into());
                 vals.push(Value::String { val: c, span: head });
 
@@ -157,6 +163,12 @@ fn help(
                     span: head,
                 });
 
+                cols.push("is_plugin".into());
+                vals.push(Value::Bool {
+                    val: cmd.2,
+                    span: head,
+                });
+
                 cols.push("usage".into());
                 vals.push(Value::String { val: c, span: head });
 

crates/nu-command/src/core_commands/register.rs

@@ -21,6 +21,7 @@ impl Command for Register {
                 SyntaxShape::Filepath,
                 "location of bin for plugin",
             )
+            .optional("signature", SyntaxShape::Any, "plugin signature")
             .category(Category::Core)
     }
 

crates/nu-command/src/default_context.rs

@@ -146,7 +146,7 @@ pub fn create_default_context() -> EngineState {
         working_set.render()
     };
 
-    engine_state.merge_delta(delta);
+    let _ = engine_state.merge_delta(delta);
 
     engine_state
 }

crates/nu-command/src/example_test.rs

@@ -33,7 +33,7 @@ pub fn test_examples(cmd: impl Command + 'static) {
         working_set.render()
     };
 
-    engine_state.merge_delta(delta);
+    let _ = engine_state.merge_delta(delta);
 
     for example in examples {
         // Skip tests that don't have results to compare to
@@ -53,7 +53,7 @@ pub fn test_examples(cmd: impl Command + 'static) {
             (output, working_set.render())
         };
 
-        engine_state.merge_delta(delta);
+        let _ = engine_state.merge_delta(delta);
 
         let mut stack = Stack::new();