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>
Implemented `treatComments` option

The manual has not yet been adapted. Proposed addition:

```latex
\item[\verbitem{treatComments}] \lstinline!0!

When this option is set to \lstinline!1!, commented lines get a special
treatment. While they rest indented, all comment symbols (\%) in those lines
will get stacked and there will be at max one space after each set of comment
symbols. This option may be useful when \lstinline!latexindent.pl! is run
several times on the same file, while lines in that file are being commented/
uncommented in the meantime. In such a situation those lines may become ugly.
The usefulness of this option depends on your workflow.
```

Signed-off-by: Michel Vosskuhle <m.vosskuhle@uni-muenster.de>