Fix union method in MathInterval.
Union method now returns false when it's not possible to perform a union.
First workd towards the creation of MathIntervalExpression
Contribute to #4 and fix #1.
Add MathIntervalCollection to handle expressions. Contructor and union
method are implemented. Union/intersection methods now accept different
types as input.
Fix #4. Correct union method.
Merge branch 'master' into feature/4_correct_unions
Update documentation and version bump.
Merge pull request #5 from danielfdsilva/feature/4_correct_unions

Feature/4 correct unions