`gpos` `pos` positional count begins at 1 when should be Pythonic 0

The gpos function requires an integer argument pos to define the plot position. The first position is encoded by the value 1, but this is very un-Pythonic, since 0 which encodes the first position for mots of not all Python objects. In practice, this can making programmatic usage awkward, for example when iterating over something to assign sub-plots, a value i + 1 needs to be used instead of simply i, which would be much cleaner and understandable to those reading the code:

for i, proj in enumerate(<variable to change across subplots>):
    cfp.gpos(i + 1)
    <generate sub-plot with given variable choice>

So, we should set the position pos to being at 0 and count from there, not from 1. The pos argument could also be documented much more clearly, so this should be done when this change is made.