Add type signatures for subfunctions of `block`.
Document behavior of `notFollowedBy'`.
Style.
Get rid of some instances of `() <$`.
Comments.
`notFollowedBy` vs. `notFollowedBy'`.
Style.
Use `addTrailingNewline` when reading Markdown.
Get rid of the “add \n\n to everything” hack.

  * Now blocks can be terminated by EOF.
  * Fixed some tests which were relying on previous behavior.
Remove `optional newline`.

Seemingly needless.
Comments.