log likelihood and derivatives for chi-squared distribution

`llikChisq(x, df, full = FALSE)`

- x
variable that is distributed by chi-squared distribution

- df
degrees of freedom (non-negative, but can be non-integer).

- full
Add the data frame showing x, mean, sd as well as the fx and derivatives

data frame with `fx`

for the log pdf value of with `dDf`

that has the derivatives with respect to the `df`

parameter
the observation time-point

```
llikChisq(1, df = 1:3, full=TRUE)
#> x df fx dDf
#> 1 1 1 -1.418939 0.63518142
#> 2 1 2 -1.193147 -0.05796576
#> 3 1 3 -1.418939 -0.36481858
llikChisq(1, df = 6:9)
#> fx dDf
#> 1 -3.272589 -0.8079658
#> 2 -4.126989 -0.8981519
#> 3 -5.064348 -0.9746324
#> 4 -6.072899 -1.0410091
```