Added the newly created volk_gnsssdr module

The volk_gnsssdr is just created. This module is the original one,
obtained with volk_modtool. The steps to create this module are (note
that gnuradio and gnss-sdr projects from github are cloned to
/Users/andres/Github/gnuradio and /Users/andres/Github/gnss-sdr):
1) export PYTHONPATH=/Users/andres/Github/gnuradio/volk/python
2) cd /Users/andres/Github/gnuradio/volk/python/
3) ./volk_modtool -i
name: gnsssdr
destination: /Users/andres/Github/gnss-sdr/src/algorithms/libs
base: /Users/andres/github/gnuradio/volk