IndexFile parser for .shx files.
For now, the creation of index files is done in the ShapefileWriter. But this can be used to
access the index.
For details on the index file, see "ESRI(r) Shapefile - A
Technical Description"
Implements an algorithm to compute the sign of a 2x2 determinant for double precision values
robustly. It is a direct translation of code developed by Olivier Devillers.
Not much but a type safe enumeration of file types as ints and names. The descriptions can easily
be tied to a ResourceBundle if someone wants to do that.