The main use case of DjHTML is to modify files in-place. Therefore, the `-i`
(`--in-place`) argument has been made the default and removed, leaving only
a deprecation error. The `-o` (`--output-file`) argument has also been
removed.

Reading from standard input and writing to standard output is still
supported by using "-" as the filename. By the same mechanism, writing the
output to a different file is also still possible by using output
redirection:

    djhtml - < input.html > output.html

Since this is a backwards-incompatible change, the next release will
increment the major version number. No changes have been made to the
indentation algorithm.

Closes #66
Closes #69
Closes #70