Import discount-2.1.6 as textproc/discount, packaged for wip
by zecrazytux and fhajny.

Markdown is a text-to-HTML conversion tool for web writers. Markdown
allows you to write using an easy-to-read, easy-to-write plain text
format, then convert it to structurally valid XHTML (or HTML).

The overriding design goal for Markdown's formatting syntax is to make
it as readable as possible. The idea is that a Markdown-formatted
document should be publishable as-is, as plain text, without looking
like it's been marked up with tags or formatting instructions. While
Markdown's syntax has been influenced by several existing text-to-HTML
filters, the single biggest source of inspiration for Markdown's
syntax is the format of plain text email.

Original Markdown implementation is written in Perl. Discount provides a
Markdown CLI tool and a library, written in C.
+ discount.
Added textproc/discount version 2.1.6