Menu and Desktop icon to launch an OSGeo4W command shell suitable for commandline utilities (GDAL, PROJ, etc).

 * Installs `osgeo4w.bat` and creates link on Desktop
 * installs `bin\o-help.bat` - a quick report of the available programs (pretty prints bin/*.exe, *.py)

Spawned from ticket #18

== Changes==
=== 1.0.0-2 --> .0-3 ===

 * fixed bug in postinstall: Start menu one link was not created properly
 * osgeo.bat calls o-help on startup
 * Shortened osgeo-help.bat to o-help.bat (if you upgraded from .0-2 you may need to remove the old one manually)