Trim get_inflator / get_deflator from POD.

get_inflator() and get_deflator() are not implemented.
Change add_(?:inf|def)lator from set_(?:inf|def)lator in POD.

Teng::Schema::Table#set_inflator() (and that for deflator) are not implemented.
Instead, add_inflator() and add_deflator() are defined.
Merge pull request #119 from dayflower/fix_table_pod

Fix POD for APIs of Teng::Schema::Table