relax SVN archive

The symbols are now also coloured in write_xy_header().

Set colours can now be specified in write_xy_header().

In write_xy_header(), the legend box can be now turned on or off and can have its position set.

Changed the handling of the [None, None] format args.

These now default to None and are converted to [None, None] inside the function.

The paper size of A4 can now be set in write_xy_header().

The tests list is now optional.

Individual system tests can now be executed through the relax test suite.

Passed self.tests into the run() method instead of the class __init__() method.

Finished the __init__() docstring and passed the tests arg into the system tests.

Test_suite_runner now has an __init__() method and stores the list of tests.