made evaluate method exported

[AndrewChubatiuk]

PR makes evaluate method exported to allow evaluation of different parts of already parsed expression.
E.g: with data{A: "a", B: ""} want to transform

Or {
  Is Not Empty {
    Selector: A
  }
  And {
    Is Empty {
      Selector: A
     }
     Is Not Empty {
      Selector: B
     }
   }
 }

into

Is Not Empty {
  Selector: A
}

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