Fix #17 and explicitly initialize PostcohInspiralTable fields to 0

The old version resulted in slightly different sngl_far columns for Virgo in zerolags. They were 0, instead of 0.0
To fix this, we should initialize the memory of sngl_fars (and other columns if appropriate) to 0

Fix #17 (closed): segfault due indexing out-of-bounds in multistats

See merge request !40 (merged)

(cherry picked from commit 51cc9032)

906e3a95 Use stats_idx when accessing multistats 2b9840cc Use element->enabled_ifos for num_stats b42b685c Refactor using the pattern described by #3