Get CMake to search for GSL
Give a more sensible implementation for derivxy in bilinear case
Typo in file test.c
Merge pull request #2 from vijaygopalchilkuri/master

Typo in file test.c
Switch to a more robust GSL locator for CMake
Remove unused variable in interp2d_eval_impl
Add interp functions without boundary checks

This commit adds functions to perform interpolation at points which
may be outside of the interpolation region. Functions to evaluate the
derivatives outside the interpolation region are planned.