relax SVN archive

Fix for the specific API common method _return_value_general() for when spectrum IDs are not present.

Not sure why this change is necessary! This could introduce future bugs, or hide a new bug!

Updated the arg_check.is_func() function for handling class methods.

Fix for the function checking in the specific API Param_list objects.

Class methods were not being detected!

Fix for the specific API _return_conversion_factor_spin() method.

The wrong variable was being used.

Fix for the initialisation of the conversion factor storage in Param_list.

Removed spin args from return_conversion_factor() and added optimisation parameters.

The global and spin specific optimisation parameters are now set up for all specific analyses.

Created the specific function API _return_conversion_factor_spin() method.

The Param_list.get_units() method can now handle function type objects.

This is needed for the model-free Rex parameter.

Fix for the Param_list.get_conv_factor() method - the function type was not properly handled.

Added the ability to store and return conversion factors in the Param_list specific API object.

This includes accepting functions so that factors requiring user loaded data can be supported.