implement complete metabolism

[stolsky]

• [x] stomach
• [x] test ingestion
• [x] add Digestion -> organic food is harder to digest
• [x] rectum (relation with Energy)
• [x] improve mass (required Bar)
• [x] add Ingestion
• [x] implement organic food is harder to eat (assume fights, etc.) moved to #14
• [x] Simulation's vanish (consumed by) -> mass.now = mass.min
• [x] Simulation's defecate -> rectum.now = rectum.max
• [x] Simulation's dying -> no energy
• [x] fix vanishing mass -> count stomachs also!!