Ordered lists always start with 1, regardless of starting number in markdown

[paulroub]

Marked version: 0.3.17

Markdown flavor: CommonMark

Expectation

Ordered lists should start with the number used to begin the list in markdown. e.g. given:

3. One
4. Two

We should see:

<ol start="3">
<li>One</li>
<li>Two</li>
</ol>

Result

We always start at 1.

<ol>
<li>One</li>
<li>Two</li>
</ol>

What was attempted

Appears to be the root cause of an issue logged for Atom's markdown-preview plugin: atom/markdown-preview#502

References:

CommonMark, Lists:

The start number of an ordered list is determined by the list number of its initial list item. The numbers of subsequent list items are disregarded.

(see also the examples in that section)

The GFM specs carry this requirement over.

[joshbruce]

@paulroub: Thank you for submitting this and the related PR solution. See the PR comments.