Better exception handling for something that seems to sometimes fail (wrt. Dataset from Netcdf4 library)

Changes to allow for less strict testing of extent, 2D NetCDF rasters, smart searching of a unique value in a raster etc.

Some problems were solved; some properties were added to a base class; attempt to enable installation by means of pip

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More changes were applied to make the code suitable for Python 3. In addition, a test module was started.

The packages tables and netCDF4 seem to require a special version of numpy. As a result, the import of included modules which require tables / netCDF4 were given errors and have been commented out for the meantime.

Method copyToMemory renamed to copy_to_memory in order to conform to the style used elsewhere in the package

A library to copy a raster into memory. This is esp. useful for raster types such as TileTiffRaster which seem not to support repeated reading

This is a library for "punching through" a raster - e.g. in the centre point of a grid cell - to see whether that point is located within an underlying shape or not. So far it's only working with shape files.

A code block in the cliplib was surrounded with "try" and "finally" to make sure the raster is always reset whatever happens.

Conflicts:
	README.md