Evaluation of True/False statements

[jimc101]

There is a mixture of syntax used in evaluating truth statements which needs addressing. Need to double check Cython interprets all of them in the same way. Even if it does, it makes sense to use a uniform syntax. A prime example is grid_metrics.pyx, where one sees statements like if var == True: and if var: mixed. Especially important is not confusing this syntax with comparisons to None.