Documentation fix.
OI_ARRAY tables are now merged.

Previously oimerge would create a merged dataset without any OI_ARRAY
tables (this is valid OIFITS v1). Merged output now includes OI_ARRAY
tables. In simple cases, only a subset of the input array tables are
copied and some output data tables will refer to a compatible array
(one with near-identical coordinates and identical station indices to
the original.