Add dependency on ansi-wl-pprint.
Initial port to ansi-wl-pprint (#11).
Fix empty check for Chunk.
Split header and usage in ParserHelp.
Use indent instead of nest.
Restore error messages in help.
Remove commented out code.
Minor fixes to help generation.
Append newline when testing help text.
Ensure trivial alternatives have no parentheses.
Restructure modules.
Bump version to 0.7.0.
Avoid importing pprint module directly.
Automatically word wrap descriptions.

Now all the fields that might have to be formatted have type `Chunk
Doc`, and their builders create them using `paragraph`, so that they can
be automatically word-wrapped.

I also added alternative builders that take a `Maybe Doc` instead of a
string, which might be useful for descriptions that require special
formatting.
Add number of columns as a preference.
Format usage line (fix #45).
Refactor help generation.
Make execParserPure purer.

The `execParserPure` function now returns a pure value in case of parser
failure.

Since completers operate in the IO monad, when a parser's completion facilities
are used, `execParserPure` still returns a value which can only be inspected in
the `IO` monad.
Add local type signatures in BashCompletion.
Restrict types of value and metavar (fix #46).