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*January 25, 2015*
* Changed license to New BSD.
* Added support for point-specific and masked-grid kriging. Note that the arguments for the `OrdinaryKriging.execute()` and `UniversalKriging.execute()` methods have changed.
* Changed semivariogram binning procedure.
* Boosted execution speed by almost an order of magnitude.
* Fixed some problems with the external drift capabilities.
* Added more comprehensive testing script.
* Fixed slight problem with `read_asc_grid()` function in `kriging_tools`. Also made some code improvements to both the `write_asc_grid()` and `read_asc_grid()` functions in `kriging_tools`.