Optional link wrapping

[gusrub]

Hi!

I'm not sure if you accept patches but I came across a specific need to have the links not wrapped and did some changes to the code.

Basically the gem turns links like this:

<a href="https://example.com">This is a link!</a>

Into this:

[This is a link!](https://example.com)

We need to have a fully text-only version of certain html that we add for descriptions for calendar ICS integration and the markdown-like syntax kinda seems broken/off into said descriptions.

I added an optional wrap_links argument that defaults to true so the existing implementation does not break for anyone but if you pass false to the initializer or the convert method then you would get something like this instead:

This is a link!: https://example.com

Which suits or needs and probably others.

Also updated the SPEC's to include a test case for this.