Changed variables to protected

It would be nice to have variables as protected, to inherit class
merged branch yosmanyga/patch-1 (PR #181)

This PR was submitted for the 2.0 branch but it was merged into the 2.1 branch instead (closes #181).

Discussion
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Changed variables to protected

It would be nice to have variables as protected, to inherit class.

Commits
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edf2e00 Changed variables to protected