Update parse errors for tree construction tests

I've gone through nearly all the tree construction tests and updated the parse errors.

My method was to take each test and compare the number of reported parse errors between html5lib-python and the parser I'm working on. Where they agreed, I simply pasted html5lib-python's errors in. Where they disagreed, I stepped through with the spec in hand and tried to tease out the proper errors. (Sometimes html5lib-python looked right. Sometimes my parser looked right. Sometimes neither looked right. And I'm sure I didn't get them all right, but I think it's a good deal better than nothing.) Note that although the *number of errors* for a given test may be agreed upon between the two parsers, I did not verify that those errors are *accurately described*.

I have not yet done tests09 and tests10. I'll add them later, in this or another pull request.

I did delete one test: the fifth test in tests18. It was an exact duplicate of the fourth test in tests18.

Whenever I resolved disagreements between the parsers against html5lib-python, I took notes. They're available [in this gist](https://gist.github.com/nolanw/3d95ce9fd9620b060575) in hopes that they may be helpful. I numbered the tests in each file starting with zero, as they were before any commits in this pull request.

Fixes #14 (and then some).