relax SVN archive

Implemented the specific_analyses.relax_fit.optimisation.d2func_wrapper() function.

This converts the numpy parameter array into a Python list, calls the
target_functions.relax_fit.d2func() function with this list, converts the Hessian output list of
lists into a numpy rank-2 array, and returns it. This will allow Newton optimisation to be used for
the relaxation curve-fitting analysis.

The square() function macro is now defined for the target_functions/exponential.c file.

This is defined in the header, and now the exponential.h is included in the C file to access it.

Implemented the exponential curve second partial derivative C functions.

These are declared in the exponential.h header file and are now used by the Python function
target_functions.relax_fit.d2func().

Partly implemented the front end target_functions.relax_fit.d2func() C module Python function.

This is not fully implemented as the exponential curve double partial derivatives are not
implemented.

Comment fixes and formatting changes in all of the target_functions C files and headers.

Comment fix in the target_functions/c_chi2.c file.

Clean up of the header and includes of the target_functions/c_chi2.c file.

The square() function macro has been shifted to the header file and the stdio.h and math.h standard
library headers are no longer included as they are not used.

The target_functions/exponential.c file no longer includes exponential.h.

This is not needed as exponential.h only contains the function definitions of the exponential.c
file.

All of the C code chi-squared functions now have the array argument dimensions explicitly declared.

Better commenting in the C header files.