Added basic support for CORRNAME and CORRINDX_* in existing tables.

Implemented reading and writing 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 and writing of optional RVIS, RVISERR,
CORRINDX_RVIS, IVIS, IVISERR and CORRINDX_IVIS columns in OI_VIS. This
has not yet been tested.