Added position interpolation (#41)

* added environment file

* Added GSL

* Fixed travis.yml:

* Maybed actually fixed travis

* More travis fixes

* interpolation now compiling

* Added tests

* added interp tests

* now building

* Added better cubci spline test

* Added exceptions

* Check for openblas error on linux

* Force openblas update?

* Trying to get a better openblas version

* Checking conda version

* Specify openblas version?

* Added tests to travois

* Moved interpolation into separate methods

* Added better interpolation tests