Progagate errors from C-API #4
Description
Currently errors are caught, but not disambiguated. When calls to libfes return a non-zero (or actually 1), there is the option to ask libfes for a clarification using either fes_error (returns string) or fes_errno (returns int/enum). It would be nice to use this functionality to give the user of gofes better errors.
See https://bitbucket.org/cnes_aviso/fes/src/master/C_API.rst for details!