relax SVN archive

Removed some old code.

Added some missing imports.

Fixed the unit tests for dchi2_element and d2chi2_element.

Two new unit tests have been added for the dchi2 and d2chi2 functions as well.

Fixed the model-free optimisation code to use the dchi2_element and d2chi2_element functions.

Overhaul of the chi-squared gradient and Hessian functions.

The original functions have been renamed to dchi2_element and d2chi2_element as these calculate the
gradient for element j and the Hessian for element {j, k}. Two new functions, dchi2 and d2chi2 have
been written to calculate the full gradient and Hessian in one function call.

These changes will temporarily break a lot of code!

Improvements to the chi-squared value, gradient, and Hessian docstrings.

Fixes for the alignment tensor gradient function code.

Wrote functions for all the alignment tensor gradients.

Import fixes.

Split the rdc module in half, shifting the alignment tensor components into their own module.