lennard_jones: Add higher-order derivatives functions

In order to be able to generate interpolation coefficients for the
interpolation schemes, add the higher-order derivative function.
Add helper module to generate the coefficients for an interpolation scheme

In order to simplify the coefficient generation for the interpolation
schemes, tabulated_generator can generate the lattice with the
interpolation coefficients for a given potential.

Currently, only a host implementation is available. But since this
calculations needs to be done only once and coefficients can be stored
and loaded from a H5MD file, this should not be a bottleneck.
lennard_jones: add tabulated_generator instantiations
Add a tabulated_force example

This example shows how to make an external potential using the tabulated
force module. The generate_coefficients.lua script generates the
interpolation coefficients and the potential while the tabulated_force.lua
will load these coefficients and simulate the system.
lua: provide offset_to_multi_index() and multi_index_to_offset()

These functions work identically to their C++ counterparts from
utility/multi_index.hpp and provide a mapping from a multi dimensional
index into an offset and vice versa.
numeric/operators: use ceilf()/floorf() when using float
lua/numeric: add numeric.diag() to return diagonal elements in a matrix