Add ignore_private option

[st0012]

Assume we have a class like:

class Operation
  def extras
    dig_attribute("extras")
  end

  private

  def data
    @data
  end

  def dig_attribute(attr)
    data.dig("attributes", attr) 
  end
end

Every time we call extras, it'll call dig_attribute and data as well. So the output of print_calls(operation) would look like this

As you can see, the entries of private helpers like data and dig_attribute provide duplicated or redundant information.

So we should have an option to filter out calls of private helpers.

print_calls(operation, ignore_private: true)