fixup! API: Include the region of the match, not just the position

(Minor documentation tweaks)
Fix display of `Region` documentation in man page

In my terminal, `man stbt` was showing this:

      01234567890123
    0 aaaaaaaa
    1 aaaaaaaa
    2 aaaaaaaa
    3 aaaaaaaa
    4 aaaaaaaaaaaca
    5 aaaaaaaaaaaaa
    6 aaaaaaaaaaaaa
    7 aaaaaaaaaaaaa
    8     aaaaaabaa
    9     aaaaaaaaa

Instead of this:

    0 ░░░░░░░░
    1 ░a░░░░░░
    2 ░░░░░░░░
    3 ░░░░░░░░
    4 ░░░░▓▓▓▓░░▓c▓
    5 ░░░░▓▓▓▓░░▓▓▓
    6 ░░░░▓▓▓▓░░░░░
    7 ░░░░▓▓▓▓░░░░░
    8     ░░░░░░b░░
    9     ░░░░░░░░░

(Those solid block characters are outside of 7-bit ascii.)
Fix display of `Region` documentation in web page

Unlike the man page (generated by rst2man), the web version at
http://stb-tester.com/stbt.html is generated by pandoc. Pandoc
requires that each line in an indented code block be indented
at least as much as the first line.