Added implementation for r_set_remove() according to documentation in set.h header
Fixup: member accessing
Fix: The hashtable should calculate the hash on its own
Fix: The hashtable should calculate the hash
Fix: The hashtable calculates the hash
Merge pull request #184 from matthiasbeyer/implement-r_set_remove

Added implementation for r_set_remove()
Added implementation for r_set_contains()