move write_coefficients to interpolator
add c function generator for periodic grids
add c function generator for generic grids

also, some niceties in the way this is used in the final C file that the
interpolator writes.
add interpolation sum

supposedly this should work. now I just have to test it.
add methods to compile shared library for interpolator
fix cinterpolate so there's no segfault
remove all segfaults

resulting plot is smooth, and there are no segfaults for arbitrary
dimensions of the input array.
finish up clib

some minor aesthetical thing, and testing with the channel database
works.
TODO:
put a test in examples, and test the derivatives too.
add wrapper for getRaw type calls
add test for interpolation

and for rawData, although I'm not sure that one makes any sense...
minor fix: title for interp test axes
Merge branch 'splines-ctypes-acceleration' into develop