panel.fishmaps: A lattice panel function
In fernandomayer/FishMaps: Plots Fishery Data into Maps

A lattice panel function to draw rectangles where z is different from zero and to draw points where z is exactly zero.

1 2	panel.fishmaps(x, y, z, map.db, msq, breaks, col.land, col.reg, labsx, labsy, subscripts, ...)

`x`	From lattice formula x.
`y`	From lattice formula y.
`z`	From lattice formula z.
`map.db`	The map database.
`msq`	The middle of squares defined in argument `square` in `levelmap`.
`breaks`	The `breaks` argument from `levelmap`.
`col.land`	The land color, from `levelmap`.
`col.reg`	The color regions, from `levelmap`.
`labsx`	The x axis ticks and labels.
`labsy`	The y axis ticks and labels.
`subscripts`	Lattice panel subscripts.
`...`	Other arguments passed to lattice panel functions.