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/static_field/closure.wren

@@ -11,6 +11,6 @@ class Foo {
 }
 
 Foo.initialize
-IO.print(Foo.closeOverGet.call) // expect: Foo field
-Foo.closeOverSet.call
-IO.print(Foo.closeOverGet.call) // expect: new value
+IO.print(Foo.closeOverGet.call()) // expect: Foo field
+Foo.closeOverSet.call()
+IO.print(Foo.closeOverGet.call()) // expect: new value