Fix to parse table rows with escaped '\|'

[mingodad]

This is a fix to allow correctly parse tables with vertical bar escaped see bellow from https://github.com/mity/md4c :

Column 1 | Column 2
---------|---------
foo      | bar
baz      | qux \| xyzzy
quux     | quuz
.
<table>
<thead>
<tr><th>Column 1</th><th>Column 2</th></tr>
</thead>
<tbody>
<tr><td>foo</td><td>bar</td></tr>
<tr><td>baz</td><td>qux | xyzzy</td></tr>
<tr><td>quux</td><td>quuz</td></tr>
</tbody>
</table>