1. Corrects a bug with `strget()` not properly returning EOF
       because it was returning a `char` or `unsigned int` instead
       of an `int` (should be a `signed int`, but that way lies C99
       madness.)   This bug was reported by A.S.Bradbury, who discovered
       it when trying to build markdown with a 64 bit version of gcc.
    2. Corrects a boundary condition bug with `![]()` and/or
       `[]()`, where the content parser stops parsing 4 (for IMG) or 5
       (for HTML) characters before the end of the embedded content.
       This bug was reported by Christian Herenz, who has been finding
       many many boundary condition bugs in the way `![]()` and `[]()`
       (don't) work.
    3. Adds a small feature; the configuration option `--enable-superscript`
       makes discount fancypants `word^word` into `word<sup>word</sup>`.