Calculates the coordinates of a proportional point of the figure region in user units.

`getFigCtr(pos=c(0.5,0.5))`

A two element vector containing the coordinates of the center of the figure region in user units.

- pos
The proportion of the figure region to find (see Details).

Jim Lemon (thanks to Karl Brand for the adjustable coordinates)

`getFigCtr` reads parameters about the current plot and calculates the
vertical and horizontal centers of the figure region by default. This is
typically useful for placing a centered title on plots where the left and
right margins are very different.

By changing `pos`, any proportional points of the figure region can be
returned. For example, `pos=c(0,0)` will return the left and bottom
coordinates of the figure region.