Rename input variables for increased clarity

[kmongird]

The following cerf input variables should be renamed:

current variable name	new variable name
capacity_factor	capacity_factor_fraction
carbon_capture_rate	carbon_capture_rate_fraction
fuel_co2_content	fuel_co2_content_tons_per_btu
fuel_price	fuel_price_usd_per_mmbtu
fuel_esc_rate	fuel_price_esc_rate_fraction
heat_rate	heat_rate_btu_per_kWh
lifetime	lifetime_yrs
unit_size	unit_size_mw
variable_om	variable_om_usd_per_mwh
variable_cost_esc_rate	variable_om_esc_rate_fraction
carbon_tax	carbon_tax_usd_per_ton
carbon_esc_rate	carbon_tax_esc_rate_fraction

Note that the units follow what cerf uses in its equations after all conversions (whether internal or external) occur. If the internal conversions are removed from the model, these names should still be consistent with what cerf expects.

[kmongird]

@crvernon

Additional variable renaming:

current variable name	new variable name
locational_marginal_pricing	locational_marginal_price_usd_per_mwh
generation	generation_mwh_per_year
operating_cost	operating_cost_usd_per_year
net_operational_value	net_operational_value_usd_per_year
interconnection_cost	interconnection_cost_usd_per_year
net_locational_cost	net_locational_cost_usd_per_year