allow unsafe and ref in grammar

`unsafe` and ref returns are allowed for delegates, local functions, and methods. Update the grammar for that part.

Fixes #886

See #941 (review)

Author: BillWagner

standard/classes.md

@@ -1930,7 +1930,6 @@ method_header
 method_modifier
     : ref_method_modifier
     | 'async'
-    | unsafe_modifier   // unsafe code support
     ;
 
 ref_method_modifier
@@ -1945,6 +1944,7 @@ ref_method_modifier
     | 'override'
     | 'abstract'
     | 'extern'
+    | unsafe_modifier   // unsafe code support
     ;
 
 return_type

standard/delegates.md

@@ -13,7 +13,7 @@ A *delegate_declaration* is a *type_declaration* ([§14.7](namespaces.md#147-typ
 ```ANTLR
 delegate_declaration
     : attributes? delegate_modifier* 'delegate' return_type delegate_header
-    | attributes? ref_delegate_modifier* 'delegate' ref_kind ref_return_type delegate_header
+    | attributes? delegate_modifier* 'delegate' ref_kind ref_return_type delegate_header
     ;
 
 delegate_header
@@ -22,16 +22,12 @@ delegate_header
     ;
     
 delegate_modifier
-    : ref_delegate_modifier
-    | unsafe_modifier   // unsafe code support
-    ;
-
-ref_delegate_modifier
     : 'new'
     | 'public'
     | 'protected'
     | 'internal'
     | 'private'
+    | unsafe_modifier   // unsafe code support
     ;
 ```
 

standard/statements.md

@@ -447,7 +447,7 @@ A *local_function_declaration* declares a local function.
 ```ANTLR
 local_function_declaration
     : local_function_modifier* return_type local_function_header local_function_body
-    | ref_kind ref_return_type local_function_header ref_local_function_body
+    | ref_local_function_modifier* ref_kind ref_return_type local_function_header ref_local_function_body
     ;
 
 local_function_header
@@ -456,8 +456,12 @@ local_function_header
     ;
 
 local_function_modifier
-    : 'async'
-    | unsafe_modifier   // unsafe code support
+    : ref_local_function_modifier
+    | 'async'
+    ;
+
+ref_local_function_modifier
+    : unsafe_modifier   // unsafe code support
     ;
 
 local_function_body