compak_evalkernel: Calculates the kernel at a key point
In thomas-fung/compak: Conway-Maxwell-Poisson Associated Kernel

This function evaluates the kernel, which is centred at key, over a grid of points using the counts provided in a list.

1	compak_evalkernel(key, counts, x, nu)

`key`	character: where the kernel should be centred.
`counts`	list of distinct count values; names are the observed values; elements are the corresponding frequencies
`x`	numeric vector :the points of the grid at which the density is to be estimated.
`nu`	numeric: CMP_mu kernel has dispersion `nu`