Add displaying information about unrecognized parameters.

Fix tab replacing.

Add gettext support.

Add support for <img/> tag for images (as an option).

Check whether input file and stylesheet files were found.

Enable downloading stylesheets and input files when url specified
(later).

Consider renaming some parameters.

Enable choosing page language.

Consider adding built-in stylesheets to the program.

Add support for <abbr> tag for most common used abbreviated forms (as
an option). Users should be able to specify them.

Consider adding (as an option) support for <hr/> tag. For example, if
line starts with '---' or '-- ', the whole line is replaced by
<hr/>. User shoulds be able to specify characteristic strings.

Fix issues with some chars.

Consider adding information about generator.

Enable adding W3C "Valid XHTML!" button, and, if user didn't include or link
his own stylesheets, "Valid CSS!" button at the bottom of the document.