getPropUsed: getPropUsed
In syanco/checkyourself: Simulates a simple agent-based species distribution model

Function to get the proportion of used locations (from movement model) within the habitat matching the value of 'A.coef'

1	getPropUsed(movelist, hab.mat, A.coef, matsize)

`movelist`	The list of locations visitied by agent in a single model iteration.
`hab.mat`	The habitat matrix on which the simulation was run, needs version with 1's and 'A.coef' (not probabilities of cell IDs)
`A.coef`	'A.coef' used to simulate habitat - used as key to 'hab.mat'
`matsize`	The size of one side of the square matrix on which the simualtion is run