Backport issues found

[magjac]

I ended up copying the dotparser grammar to my own project, since I needed to add line number information and whitespace, newline and comment nodes to the ast and I didn't think that that would be generally useful. During that work I found a couple of issues that I fixed without reporting them here.

You might want to have a look at https://github.com/magjac/graphviz-visual-editor/commits/master/src/dotGrammar.pegjs to see if there are any fixes you'd like to backport to dotparser.

[anvaka]

Thank you! I couldn't tell which issues are critical?

Your website http://magjac.com/graphviz-visual-editor/ looks very good though!