relax SVN archive

The major rewrite involved the Grace file writing functions. XY plots of any combination of data
for the X-axis and Y-axis can now be created. Support for Monte Carlo simulation data has also been
added.

The prompt function 'grace.view' and generic function 'view' in 'generic_fns/grace.py' have been
changed such that they will now only execute Grace. Previously the functions were also able to
create a grace file.

The regular expression doc string which is displayed in both the 'grace' and 'value' class of
functions has been moved out into its own module called 'prompt/doc_string.py'. Previously the doc
string was duplicated in both classes, the change will prevent the strings from getting out of sync.

A new Exception class called RelaxNoSimError has been added for when simulations are required but do
not exist.

The function 'return_value' in 'specific_fns/model_free.py' has been modified to return simulation
values when asked.