feat: allow empty argument list methods in calls, definitions, and docs

- Compile empty `()` as a valid method signature distinct from no parentheses
- Update `call()`, `clear()`, `run()`, `try()`, and `yield()` to use empty argument lists
- Revise documentation across multiple files to reflect new signature semantics

test/closure/assign_to_closure.wren

@@ -16,10 +16,10 @@ var g = null
   }
 }
 
-f.call
+f.call()
 // expect: local
 // expect: after f
 
-g.call
+g.call()
 // expect: after f
 // expect: after g

test/closure/close_over_function_parameter.wren

@@ -6,4 +6,4 @@ new Fn {|param|
   }
 }.call("param")
 
-f.call // expect: param
+f.call() // expect: param

test/closure/close_over_later_variable.wren

@@ -9,5 +9,5 @@ new Fn {
   new Fn {
     IO.print(b) // expect: b
     IO.print(a) // expect: a
-  }.call
-}.call
+  }.call()
+}.call()

test/closure/close_over_method_parameter.wren

@@ -9,4 +9,4 @@ class Foo {
 }
 
 (new Foo).method("param")
-F.call // expect: param
+F.call() // expect: param

test/closure/closed_closure_in_function.wren

@@ -7,4 +7,4 @@ var f = null
   }
 }
 
-f.call // expect: local
+f.call() // expect: local

test/closure/nested_closure.wren

@@ -11,11 +11,11 @@ new Fn {
         IO.print(b)
         IO.print(c)
       }
-    }.call
-  }.call
-}.call
+    }.call()
+  }.call()
+}.call()
 
-f.call
+f.call()
 // expect: a
 // expect: b
 // expect: c

test/closure/open_closure_in_function.wren

@@ -2,5 +2,5 @@
   var local = "local"
   new Fn {
     IO.print(local) // expect: local
-  }.call
+  }.call()
 }

test/closure/reference_closure_multiple_times.wren

@@ -8,6 +8,6 @@ var f = null
   }
 }
 
-f.call
+f.call()
 // expect: a
 // expect: a

test/closure/reuse_closure_slot.wren

@@ -10,7 +10,7 @@
     // Since a is out of scope, the local slot will be reused by b. Make sure
     // that f still closes over a.
     var b = "b"
-    f.call // expect: a
+    f.call() // expect: a
   }
 }
 

test/closure/shadow_closure_with_local.wren

@@ -7,5 +7,5 @@
       IO.print(foo) // expect: shadow
     }
     IO.print(foo) // expect: closure
-  }.call
+  }.call()
 }