Uppercase/mixedcase tag support for walk() function

[benjaminma]

Lowercasing encountered element names to walk <A>, <P>, <TaBLe>, etc. in walk()'s tag switch block

[mlegenhausen]

Thanks for the pull request. I will take a look.

[benjaminma]

Ah, I see. What do you think about terminating mailto: anchors and ignoring the inner text, but walking children of any non-mailto: anchor? Is the href necessary to output in those cases?

e.g. <a href="http://www.google.com">Google</a> or
<a href="#more-something"><img src="something-thumb.jpg"><div class="caption"><span>Something caption...</span></div></a>

My use case is to extract as much available text from an html doc.

[benjaminma]

I think I intended to send the PR from a feature branch. Let me see if I can split up these commits into a separate issue.

[benjaminma]

Split request. See #7 and #8.