Support single pipe comment style

[parsonsmatt]

In persistent's QuasiQuoter, you can add documentation using a -- | style doc-comment. Like in purescript, the | must be present on every comment.

-- | This is a table.
-- | This is another line of the doc comment.
SomeTable
    -- | This is a field.
    -- | This is another line of the field comment.
    someField Text

However, this requirement is odd to Haskellers, so we should support having only a single pipe.

-- | This is a table.
-- This is another line of the doc comment.
SomeTable
    -- | This is a field.
    -- This is another line of the field comment
    someField Text

This issue is done when the two code blocks create equal commentary on the produced EntityDefs.