CSVPopulation projection support.

This patch allows CSV files with projections other than WGS 84 to be used as population sources. It does this by adding an optional crs parameter to CSVPopulation. If this parameter is left out, the code behaves as it did before (that is, it is backwards-compatible); if it is present and something other than WGS 84, the individuals are reprojected. It also adds xCol and yCol parameters (which are the same as lonCol and latCol) for more idiomatic specification of non-geographic coordinate systems.