Update Documentation and fix a building error on Ubuntu
Updated some old documentation and fix isnan was not delcared in this scope
error on Ubuntu with GCC since isnan is defined differently in <math.h> and .
Tested on Ubuntu 16.04(GCC 5.4.1) and Ubuntu 14.04(GCC 4.8.1). This MR delivers issue #98 (closed) .
MR for Same issue in GDAL has also been created.