Fails to Properly Parse Nested Definition Lists

MultiMarkdown fails to properly parse nested lists. Given this MultiMarkdown:

```
homepage

: The official home of this project on the web.

bugtracker
: This entry describes the bug tracking system for this distribution. It is
a [Map](#Map) with the following valid keys:

web
: a URI pointing to a web front-end for the bug
tracker

mailto
: an email address to which bug reports can be sent

repository
: This entry describes the source control repository for this distribution.
It is a [Map](#Map) with the following valid keys:

url
: a [URI](#URI) pointing to the repository itself

we
: a [URI](#URI) pointing to a web front-end for the repository

type
: a lowercase string indicating the VCS used

: Because a URI like `http://myrepo.example.com/` is ambiguous as to type,
producers should provide a `type` whenever a `url` key is given. The
`type` field should be the name of the most common program used to work
with the repository, e.g. git, svn, cvs, darcs, bzr or hg.
```

The output is:

```

homepage

The official home of this project on the web.

bugtracker

This entry describes the bug tracking system for this distribution. It is
a Map with the following valid keys:

web

:   a <a href="#URI">URI</a> pointing to a web front-end for the bug

    tracker


mailto

:   an email address to which bug reports can be sent

repository

This entry describes the source control repository for this distribution.
It is a Map with the following valid keys:

url

:   a [URI](#URI) pointing to the repository itself


we

:   a [URI](#URI) pointing to a web front-end for the repository

type

:<dl>

a lowercase string indicating the VCS used

Because a URI like http://myrepo.example.com/ is ambiguous as to type,
producers should provide a type whenever a url key is given. The
type field should be the name of the most common program used to work
with the repository, e.g. git, svn, cvs, darcs, bzr or hg.

```

Wow. Here's what it should be (output generated by peg-multimarkdown):

```

homepage

The official home of this project on the web.

bugtracker

This entry describes the bug tracking system for this distribution. It is
a Map with the following valid keys:

web

a URI pointing to a web front-end for the bug
tracker

mailto

an email address to which bug reports can be sent

repository

This entry describes the source control repository for this distribution.
It is a Map with the following valid keys:

url

a URI pointing to the repository itself

we

a URI pointing to a web front-end for the repository

type

a lowercase string indicating the VCS used

Because a URI like http://myrepo.example.com/ is ambiguous as to type,
producers should provide a type whenever a url key is given. The
type field should be the name of the most common program used to work
with the repository, e.g. git, svn, cvs, darcs, bzr or hg.

```

Since I rely on Text::MultiMarkdown from CPAN in my Perl apps (which is directly ported from here), I can't use peg-multimarkdown ([yet!](https://github.com/fletcher/peg-multimarkdown/issues/46)). So a fix for this issue in the Perl version would be appreciated.

Thanks!

David