simplify how the nodes are passed around in build_html_tree
don't crash if there is a processing instruction at the top of the XML document
convert en-dashes to hyphens when constructing US Code links to Cornell LII, and don't encoding anything to UTF-8 because lxml.etree will reject pre-encoded bytes that contain control characters
let the URL function return None to not create a link (again)
en-dashes in Stat. citation links are page ranges but when generating the link we can only link to a page, so extract the first page in the range
handle bad data in Public Law xrefs
r3
Revert "let the URL function return None to not create a link (again)"

This reverts commit 79cc82c5fd501c5580d65ef3347ccb9e90557d60.
Remove all styling on href-less links.
Clean up comments, because I'm nitpicky.
Merge pull request #3 from JoshData/master with changes

more things