Implement leveling up character

[chanulee1]

• Implement a leveling system for the characters.
• Characters level up through experience points (XP) or milestones.
• For XP:
  • Each character has an amount of experience points (XP).
  • Once a character has enough points, they level up and gain rewards such as upgrades to their stats or new features.
• For milestones:
  • There are specific milestones (e.g., good roleplay or handling an encounter well) which, once achieved, allow the character to level up.
  • There will be a level up button on the character view screen that allows the user to update the character’s level once certain milestones are achieved.

[j618p208]

On a level up these things need to happen:

• if the class is a spellcaster, learn 2 new spells
• show the new feature
  • if that new feature is Ability Score Improvement let the player choose a feat or ability score improvement (is a feat in our database), add the choice to the feats list in the character CSV
• increase level
• HP increase, take value within the range of the character's hit dice to add to hp