Implementing a configuration framework, that can be used by SER core,

Implementing a configuration framework, that can be used by SER core,
and by the modules, to get and set internal variables on-the-fly, and
eliminate SER restarts whenever it is possible.

The core and the modules can declare configuration variables, and can
retrieve the value of the variables at any time without performance
overhead. The framework makes sure that the variables do not change
during the SIP message processing, the child processes see a snapshot
of the variables with constant values. The variable, that is changed by
a cfg driver module, will be automatically replaced by the framework
the next time a SIP message is started to be processed.

The drivers can change the value of all the variables by names with or
without the need of commit. That means a kind of transaction support,
the framework can keep track of the changes (per driver) until they
are committed or rolled-back.