relax SVN archive

Created the Frame_order.test_generate_rotor2_distribution system test.

This is to test the Frame Order distribution generating base script, used for creating the synthetic
Frame Order test data, and to demonstrate a failure in handling back-calculated RDC data.

To implement this, the test_suite/shared_data/frame_order/cam/ path has been converted into a Python
package (with the addition of the __init__.py files). The base data generation script
test_suite/shared_data/frame_order/cam/generate_base.py has also been modified to use the absolute
path for the data files and its run() method now accepts the save_path argument to allow the files
to be saved into a temporary directory.

Capitalised the pivot and CoM variables in the base frame order distribution generation script.

Created a directory for holding the CaM double rotor frame order synthetic data.

Updated the news announcement links for relax version 3.1.3 at http://www.nmr-relax.com/download.html.

The correct link is https://gna.org/forum/forum.php?forum_id=2430.

Updated the http://www.nmr-relax.com/download.html webpage for relax 3.1.3.

Updated the relax API documentation at http://www.nmr-relax.com/api/3.1/ to version 3.1.3.

Updated the relax HTML manual at http://www.nmr-relax.com/manual/index.html to version 3.1.3.

Added the relax 3.1.3 PDF manual to the repository.

Backported the relax 3.1.3 CHANGES file addition to trunk.

The command used was:
svn merge -r22014:22015 svn+ssh://bugman@.../svn/relax/tags/3.1.3 .

Updated the CHANGES file for relax version 3.1.3.