Merge pull request #5 from swtw7466/first-creature

最初の動物
Merge pull request #6 from swtw7466/add-gene

遺伝子情報追加
Avoid dispersion of type constructors: initGene
Avoid dispersion of type constructors: newDirection
Avoid dispersion of type constructors: fix doctest
Add type Plants
Add eatPlants
Creatures eat plants in each steps
Creatures have energy
initCreature
Use Array