early prototype of a language server

currently only provides hover info (but that's already quite useful for debugging)

mers_lib/src/program/run/variable.rs

@@ -79,4 +79,10 @@ impl MersStatement for Variable {
     fn source_range(&self) -> SourceRange {
         self.pos_in_src.clone()
     }
+    fn inner_statements(&self) -> Vec<&dyn MersStatement> {
+        vec![]
+    }
+    fn as_any(&self) -> &dyn std::any::Any {
+        self
+    }
 }