Bed: clean-up documentation
Table: add a Tags module (#97)
Table.Row.Tags: add `default`, `default_extension`

This is related to #97.
Tags: use Table.Row.Tags.t (#97)
Table.Row: improve APi of `of_line` (#97)
test.Fasta: fix tests
Table: update documentation (#97)
test.Table: fix test
Table.Row: add sub-module `Error`
Table.Row: add Transform.line_to_item
Table: add Transform.item_to_line (#97)
App_transform: use `Table.Row.Transform`
App_common: use `Table.Row.Transform`
Table: fix API documentation