update version
add test for storage of grid points
add functions for storage of grid points

Implement new functions to store grid points in an array of 3*N floats,
where N is the number of grid points. Grid is interpreted either as
Euclidean or as polar, depending on the new grid_type parameter.
The grid point array is intended to be used for NFFT functions.
WIP: implement forward operator
add NFFT check macros
remove whitespace
fix macro check
rename store_points_test to nfft_test
declare *_freqs functions for testing purposes
fix segfaults due to bad pointer initialization
update descriptions and add nfft3_transform function
Fix reciprocal grid error and add NFFT functions

The reciprocal grid functions did not update the is_halfcomplex
status inside the gfunc3 structure.
Functions for NFFT transform are initially written. Need debugging
due to segfaults.
make grid_reciprocal functions reject initialized gfunc3's
finalize NFFT transform - needs testing
WIP: introduce full-complex function type
rename matvec3.[ch] -> vec3.[ch]; update gnulib
update gnulib
Adapt to complex math and some further stuff

- add check for C99 compiler mode
- check for complex.h
- add check for sqrt function
rename matvec3.h -> vec3.h
WIP: Implement fully complex grid functions