Setting footnote prefix: ParsedownExtra::setFootnotePrefix( string $footnotePrefix )
	This should be a string that is valid in an HTML attribute, i.e. escaped properly.
	Default value is blank, if this is kept blank behavior is as before.
	Use case in mind is for something like a blog, where you can set the prefix to something unique like a post ID.

Added test_footnote_prefix() to test cases.

ignores the list of voided elements when rendering markdown

Stabilizes library by revamping class to utilize methods from php 5.4
or greater.

Does an extra check on valid DOMElements to make sure they have child
nodes before calling recursively.

Previously, the 'extra' in 'Markdown Extra' was only supported in links,
lists, and headings. This commits adds support for adding a class or ID
to fenced code blocks.

That'll tech me to debug my own code.

* Move the custom class to the <pre> rather than the <code>
* Add dashes in "truncated-for-brevity"
* Code language is specified through 'class="language-python"' rather than 'lang="python"'
* Remove newline at end of file

…st a `class` and `id`.

- I wanted the ability to be able to add `width` & `height` attributes to images but wasn't able to in the current state so I updated the RegEx rules and the `parseAttributeData` method. Now a user can add something like `{.test .fu #bar style="color:red; font-style:italic" data-is-cool="'tis true" lang=en_us}` and it'll render out these attributes `class="test fu" id="bar" style="color:red; font-style:italic" data-is-cool="'tis true" lang="en_us"`.
- I also added the `inlineImage` method so attributes like `width` & `height` can be added.

This can be used as a template for Parsedown extensions (like Parsedown Extra) to reuse Parsedown's original tests. You can either extend tests (like ParsedownExtraTest) or reuse them unchanged (like CommonMarkTest). Parsedown extensions simply have to implement their own TestParsedown class (test/TestParsedown.php) and all original tests will run with a instance of this class, rather than a instance of the original Parsedown class.

This PR is a follow-up to erusev/parsedown#423, i.e. you must merge erusev/parsedown#423 first, otherwise this doesn't work.

Failing tests don't break builds on purpose, Parsedown Extra doesn't fully comply with the CommonMark specs at the moment. We should switch to test/CommonMarkTest.php of erusev/parsedown later, see erusev/parsedown#423 for details.

Fixes erusev#75, erusev#84

- ext-dom is required due to the use of the DOMDocument class
- ext-mbstring is required due to the use of the mb_convert_encoding() function

…erge

…ng' into fix/merge

…ix/merge

…' into fix/merge

This reverts commit 8c0231d.

…ix/merge

…mbstring).