cumulative updates:

 - added new function ccast2rtp and helper functions cris_ichan,
   cris_vchan, guard_ind, along with some test functions

 - minor updates to finterp to match updates to iasi_decon

 - updated inst_params opts param to use an explicit field set

 - updated ccast_main and hires to use periodic sinc ILS files

 - minor updates to the main README and doc/ccast_sdr.txt