relax SVN archive

Modifications to the structure.read_pdb() user function.

The 'parser' argument has been added to allow different PDB parsers to be selected in the future.
To allow for the new relax design, the docstring has been updated with respect to the loading of the
sequence and the 'spin_id' argument has been added to allow the selection of specific atoms of the
PDB file to be placed as SpinContainers in the relax data store.

Started to create the structural object and the API for accessing, creating, modifying info.

Started to create the structure package.

The package is now initialised and has a docstring describing it. The structure module has also
been shifted from generic_fns to structure.

Deletion of the generic_fns.structure.atomic_mass() function.

The fn physical_constants.return_atomic_mass() is now used instead of the old atomic_mass() fn.

Updated physical_constants.return_atomic_mass() to better match generic_fns.structure.atomic_mass().

Created a new directory for the new 'structure' package.

This will eventually contain numerous structure related operations including:

A number of PDB parsers,
A PDB writer,
CIF parsers,
Other structural data file parsers,
Functions for creating geometric objects in structural format,
Mass and inertia related functions.

This package will eventually have a well defined API for accessing structural data independent of
the structure parser used.

Updated the generic_fns.structure.set_vector() function to the new design.

More removal of the run argument as part of the moving to the new design.

More removal of the run argument as part of the moving to the new design.