Parsing of link with underscore nested in "Emphasis" tag

[Bluezen]

Hello,

The fix for issue #14 works pretty well most of the time but it fails on special case of links with underscores in it. For example:

_Follow me on [Twitter](https://twitter.com/address_with_underscore)._

Should be rendered as:

<p><em>Follow me on <a href="https://twitter.com/address_with_underscore">Twitter</a>.</em></p>

but instead it is rendered as:

<p><em>Follow me on [Twitter](<a href="https://twitter.com/address">https://twitter.com/address</a></em>with<em>underscore).</em></p>

[Bluezen]

Actually, the issue seems to affect any tags nested in "Emphasis" tag.

_Some **Text**._

is rendered as:

<p><em>Some **Text**.</em></p>

instead of:

<p><em>Some <strong>Text</strong>.</em></p>