cfgfile: support runtime modification

cfgfile: support runtime modification

Extend existing cfgfile library with providing new API functions:

rte_cfgfile_create() - create new cfgfile object
rte_cfgfile_add_section() - add new section to existing cfgfile
object
rte_cfgfile_add_entry() - add new entry to existing cfgfile
object in specified section
rte_cfgfile_set_entry() - update existing entry in cfgfile object
rte_cfgfile_save() - save existing cfgfile object to INI file

This modification allows to create a cfgfile on
runtime and opens up the possibility to have applications
dynamically build up a proper DPDK configuration, rather than having
to have a pre-existing one.

Signed-off-by: Jacek Piasecki <jacekx.piasecki@intel.com>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>