have `oneOf` in addition of `or` in grammar and have `or|oneOf(String)`

Using `oneOf()` instead of `or()` may be readable in some grammars. Matter of taste and since the main aim of jsdl grammar is readability it makes sense to have a method with multiple names.

Also the method should work for `String` argument ˛`"abcd"` making

``` java
oneOf("abdc")
```

equivalent to

``` java
oneOf(kw("a"),kw("b"),kw("c"),kw("d"))
```
