Ressurect the ArrayColumn documentation

This reverts commit 48f3a5c3bb4b1b25e1306c93a50b30a68388c39b.
Added doc for FloatArrayColumn
Add clarification that Float/Double/Long are 32/64/64 bits
Remove long from values type since it applies to multiple column types
fixed width -> fixed-width
Merge pull request #279 from manics/tables_arraycolumns_9957-2

Tables ArrayColumn docs 9957