pkienzle/periodictable: v1.6.0

Documentation: http://periodictable.readthedocs.org/en/v1.6.0

New:

• Add energy dependence for rare earths (Lynn and Seeger, 1990).

Modified:

• Use complex b_c when computing the coherent cross section, leading to correct values of sigma_c and sigma_i for materials with large absorption. With this change the tabulated values for B[10] are now shown to be self-consistent within a few percent.

Breaking changes:

• Neutron scattering factors are returned with one value for each wavelength even for energy independent elements. Previous versions returned a scalar if the returned value was identical for each wavelength.

See README.rst for complete history.