add monthly normalized env

[jiangjingzhi2003]

The code to merge is for the normalized monthly environment which action are normalized between -1 and 1.

I also plot the greencrab population change overtime for non-normalized month environment when action = [0,0,0]

the image above is for crab size 0


the image above is for crab size 7

I also plot the greencrab population change overtime for non-normalized month environment when action = [0,0,0]
Please let me know if the population change for monthly environment is reasonable or not.

[felimomo]

looks good!!