* Added Text.Pandoc.Pretty.
This is better suited for pandoc than the 'pretty' package.
One advantage is that we now get proper wrapping; Emph [Inline]
is no longer treated as a big unwrappable unit. Previously
we only got breaks for spaces at the "outer level." We can also
more easily avoid doubled blank lines. Performance is
significantly better as well.
* Removed Text.Pandoc.Blocks.
Text.Pandoc.Pretty allows you to define blocks and concatenate
them.
* Modified markdown, RST, org readers to use Text.Pandoc.Pretty
instead of Text.PrettyPrint.HughesPJ.
* Text.Pandoc.Shared: Added writerColumns to WriterOptions.
* Markdown, RST, Org writers now break text at writerColumns.
* Added --columns command-line option, which sets stColumns
and writerColumns.
* Table parsing: If the size of the header > stColumns,
use the header size as 100% for purposes of calculating
relative widths of columns.
