Implemented `removeTrailingWhitespace` option

The manual has not yet been adapted. Proposed addition:
```latex
\item[\verbitem{removeTrailingWhitespace}] \lstinline!0!

By default \lstinline!latexindent.pl! indents every line --also empty lines--
thus creating `trailing whitespace' feared by most version control systems. If
this option is set to \lstinline!1!, trailing whitespace is removed from all
lines, also non-empty ones. In general this should not create any problems, but
by precaution this option is turned off by default.
```

Signed-off-by: Michel Vosskuhle <m.vosskuhle@uni-muenster.de>