[Users] Migration to pseudo-variables completed

[Bogdan-Andrei Iancu]

Hi folks,

All module (acc,avpops,tm,xlog) that were using pseudo-variables like 
support are finally migrated to a common pseudo-variable core (located 
in OpenSER core).

Advantages:
    consistency across current and future modules (only one definition 
scheme)
    gets red of code duplicity (easy to maintain and to fix)
    scalability - new pseudo-variables will be automatically seen from 
all modules without any additional changes

I know that this migration broke a lot of compatibilities and will force 
user to re-acustome the new pseudo-variables notacion, but this was a 
necessary step.

All the README/online-docs were update in order to give as much help as 
possible to users to adapt. For a list with supported pseudo-variables 
see http://www.openser.org/docs/pseudo-variables.html.

If you have ideas for new useful variables to be added, let us know.

regards,
bogdan