relax SVN archive

Updated the relax API manual to version 2.1.0 (http://www.nmr-relax.com/api).

Updated the relax HTML user manual to version 2.1.0 (http://www.nmr-relax.com/manual/index.html).

Added the PDF version of the relax 2.1.0 user manual to the repository.

Updated the version number to relax 2.1.0.

Merged the CHANGES file from the relax 2.1.0 tag back to the trunk.

The command used was:
svn merge -r17234:17235 svn+ssh://bugman@.../svn/relax/tags/2.1.0

Updated the CHANGES file for relax 2.1.0.

relax version 2.1.0.

This major feature release introduces the new concept of a container for data linking two atoms or
spins, the interatomic data design. This is for NMR data such as the magnetic dipole-dipole
interaction between two spins (including relaxation and RDC data) and NOESY data. As this is a
highly invasive change, modifying almost all of the relax analysis types and modifying the GUI, the
minor version number has been incremented and all of the 2.0.x version numbering has been skipped.

Fixes for the dipole_pair.read_dist user function.

Expanded RelaxNoInteratomError to handle the spin IDs as arguments, including these in the message.

Fixes for the prompt examples in the dipole_pair.read_dist user function documentation.