consider renaming diag argument in psychsyn

[awmeade]

Great package! So nice it's on CRAN now!
I was expecting the diag argument to mean 'diagonal' but i can't tell that there are any diagonals involved. perhaps renaming to something more intuitive?

[ryentes]

Yeah in retrospect that's an ambiguous abbreviation. We were discussing several alternative names for that argument. for example: "n_pairs", "count_pairs", or simply "pairs". The output column name is currently numPairs but that may change too as we have moved away from camel case in our more recent code.

I definitely welcome comments and suggestions.