v0.0.1c

Mechanics:
-class Levelling deprecated, all levelling systems are now inserted in
their respective object's class;
-Created a system common to both Active Skills and Passive Skills (enum
Skill);
-Cleaned up the code used by Passive Skills (class PassiveSkill);
-Cleaned up the code used by Active Skills (class ActiveSkill);
-Created a system common to all Active Skills and Attacks for Damage
calculations (class SkillDamage)-To be implemented;
-Created enum to hold damage types for each Active Skill and Attack
(enum DamageType);