Set DBF default character encoding to ISO-8859-1

Got some encoding problems when adding å/ä/ö in my shape data. Turns out the only supported encoding for DBF (by the original spec.) is ISO-8859-1.

There have been some extensions to the specifications and I tried to accommodate them as well.

I had to add a dependency on Iconv to decode ISO-8859-1.

This was a helpful post: http://gis.stackexchange.com/questions/3529/which-character-encoding-is-used-by-the-dbf-file-in-shapefiles