Fix tab replacing.

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 command-line options.

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 at the bottom of the
document.

Consider rewriting handling of command-line arguments with use of classes.

Add recode library support.