Minor bugs

TBRSS uses `cl-html5-parser` heavily, and I've been looking into speeding it up. These are some minor bugs I encountered while familiarizing myself with the code. 

The changes should mostly be self-explanatory, except for `parse-content-attr`, which handles an error that turned up in testing. Some poor soul had written

    <meta http-equiv="Content-Type" content="UTF-8" />

by way of a charset declaration.