Basic financing mechanism

[pksohn]

Address #52. This adds interest and fees for a construction loan to the costs for a project.

New parameters for SqftProForma object

I've added these new parameters, which become SqftProForma object attributes, in several places:

• construction_months: this and the one below are analagous to costs and heights_for_costs.
• construction_sqft_for_months
• loan_to_cost_ratio
• drawdown_factor
• interest_rate
• loan_fees

Updated cost calculation

Addition to the cost calculation is here, along with a few changes to variable names to make everything more explicit. This math precisely mirrors the way it's done in this pro forma, which happens to be very consistent with the rest of our model.

Construction time added to reference tables

I added a column for construction time based on building square footage, with configurations that allow you to tell the model how many months it should take to build a building of a given size.

• Added to the reference DataFrame for each (use, parking) pair here with this helper function modeled after this one.