Regression tests for link backtracking optimizations:

.
[[some unrelated text [link]

[link]: foo
.
<p>[[some unrelated text <a href="foo">link</a></p>
.

.
[[some unrelated text [[link]]

[[link]]: foo
.
<p>[[some unrelated text <a href="foo">[link]</a></p>
.



This is not a valid emphasis, because \n considered a whitespace:

.
**test
**

**
test**

**
test
**
.
<p>**test
**</p>
<p>**
test**</p>
<p>**
test
**</p>
.


Link label has priority over emphasis (not covered by commonmark tests):

.
[**link]()**

**[link**]()
.
<p><a href="">**link</a>**</p>
<p>**<a href="">link**</a></p>
.


Issue #55:

.
![test]

![test](foo bar)
.
<p>![test]</p>
<p>![test](foo bar)</p>
.


Should unescape only needed things in link destinations/titles:

.
[test](<\f\o\o\>\\>)
.
<p><a href="%5Cf%5Co%5Co%3E%5C">test</a></p>
.

.
[test](foo "\\\"\b\a\r")
.
<p><a href="foo" title="\&quot;\b\a\r">test</a></p>
.


Not a closing tag

.
</ 123>
.
<p>&lt;/ 123&gt;</p>
.


Not a list item

.
1.list
.
<p>1.list</p>
.


Coverage. Direcctive can terminate paragraph.

.
a
<?php
.
<p>a</p>
<?php
.

Normalize link destination, but not text inside it:

.
<http://example.com/α%CE%B2γ%CE%B4>
.
<p><a href="http://example.com/%CE%B1%CE%B2%CE%B3%CE%B4">http://example.com/α%CE%B2γ%CE%B4</a></p>
.

Autolinks do not allow escaping:

.
<http://example.com/\[\>
.
<p><a href="http://example.com/%5C%5B%5C">http://example.com/\[\</a></p>
.


Should not throw exception on mailformed URI

.
[foo](<&#x25;test>)
.
<p><a href="%25test">foo</a></p>
.