ERCOT Texas-7k load forecasts
This release resolves several issues not yet addressed in v0.4.0-a0:
- replacing the NREL load forecasts used for Texas-7k with ERCOT load forecasts, which have much less error and thus lead to less load shedding and other undesirable behaviour during simulations
- setting reserve shortfall costs to zero when calculating locational marginal prices, which helps avoid extreme prices
- fixing bug in Texas-7k minimum generator down times, which had originally been multiplied by minimum up times in the input dataset
- extended compatibility to Python 3.9 and 3.10 and added corresponding tests