calculator_presentation

Goal: Implement an observer to perform simple arithmetic operations and integrate it to Unicorn.

The observer will only accept URLs to documents described as follows:

    * Mime-type: text/plain
    * format:
          o 1 line per expression
          o an expression is composed of numbers, simple operators (+,-,*,/) and brackets, that can be combined using the regular arithmetic grammar 

Example:

For each line of this document, the observer will evaluate and return the result or throw an error.

Observer can take 2 optional parameters. The first one is to multiply results by 2. The second one is to multiply results by n.