Issue 70 - Update to pegdown-1.5.0

[rmburkhead]

Issue #70 - nb8 branch - Update pegdown to 1.5.0 (along with its requirement, parboiled, to 1.1.7). Two pegdown changes impact this module:

• LinkRenderer.Renderer href (and other fields) now final. Implemented a relatively naive copy of the rendered link when needed. This might be brittle if the LinkRenderer.Renderer class changes structure.
• Pegdown now has a token for anchor links. Added handling for them where required, using AUTOLINK as a template.

Comparing the rendered HTML output of v2.0 of the plugin to the changes made by this pull request, the only significant change seems to be that H1 headings now have a wrapped anchor link.

[rmburkhead]

Verified that both #56 and #49 appear to be resolved by updating pegdown to this version, using the markdown examples supplied in each issue.

[madflow]

This is great - thanks! The code looks fine - I'll merge it right aways to make testing easier.