v4.0.0

MimiPAGE2009 v4.0.0

Diff since v3.1.0

Merged pull requests:

• Change SCC calculation to return the net present value in the emissions year (#200) (@ckingdon95)
• Julia Package Butler Updates (#212) (@github-actions[bot])
• use equity_proportion variable for ramsey discounting (#215) (@ckingdon95)