Added ability to read CORRNAME and CORRINDX_* from existing tables.

Implemented reading of optional CORRNAME keyword and
CORRINDX_* columns in OI_VIS, OI_VIS2, and OI_T3 tables. Note that
OI_SPECTRUM does not have these in the current draft standard.

Also implemented reading of optional RVIS, RVISERR,
CORRINDX_RVIS, IVIS, IVISERR and CORRINDX_IVIS columns in OI_VIS.