Added the it99 module to the lib.dispersion package __all__ list.
This is the Ishima and Torchia 1999 2-site model for all timescales with pA >> pB.
This commit follows step 3 of the relaxation dispersion model addition tutorial (http://thread.gmane.org/gmane.science.nmr.relax.devel/3907).
Authored by: bugman 2013-06-10
Parent: [r20008]
Child: [r20010]
