calc_M1: Calculate the M1 matrix
In MartinHoldrege/precipr: Manipulating and examining precipitation intensity

Lag 1 autocorrelation and correlation of min and max temp. eq 11.22b in Wilks 2011, except wilks used covariance instead of correlation. This is eq. 7 in Richardson and Wright (1984). Since I am calculating the lagged correlation by 'hand' (not using acf()) the values are slightly (1 different (b/ of how means calculated), but I'm doing that to deal with the issue of lagging across years.

1	calc_M1(Tmax, Tmin, year)

`Tmax`	daily max temperature vector
`Tmin`	daily min temperature vector
`year`	vector of year. Year is included so lag 1 one works (not finding correlation with lagged value of the previous year)