relax SVN archive

Fixes for the relaxation curve fitting API.

The fixes are for the return_data_name(), return_grace_string(), and return_units() methods.

Docstring update to return_grace_string().

Clean up of the create_mc_data() API method across the board.

The spin_id keyword is now accepted by all, and is a keyword.

Converted the _select_model() method to be private, removing it from the API.

Converted a number of methods to being private, removing them from the API.

These include:
_grid_search_setup()
_linear_constraints()
_model_setup()
_relax_time()
_select_model()

A large number of method and documentation variables to the specific analysis API.

These include:
default_value_doc
default_value()
grid_search()
minimise()
return_data_name_doc
return_data_name()
return_grace_string()
return_units()
set_doc
sim_pack_data()

Fix for the unit test for the N-state model _disassemble_param_vector() method.

Fix for the unit test for the N-state model _assemble_param_vector() method.

Added data_names() to the specific analysis API.

General docstring clean ups as well.

Added create_mc_data() to the specific analysis API.