Added virtual destructors to each class
Due to the hierarchical nature of the code, there are a lot of derived
classes and most classes will probably have classes derived from them.
As a result, when the derived classes are deleted, there may be some
ambiguity regarding which destructor is to be called. In order to avoid
this, the desctructors of each class are defined as virtual functions.
Typographical error
Corrected the spelling of hierarchical in README.md
Merge pull request #44 from adhishm/version_0.0_simulateSingleSlipPlane_virtualDestructors

Version 0.0 simulate single slip plane virtual destructors