Table of content that works  :)

Table of content is the crucial feature for me.
So after digging in the wkhtmltopdf source, I understood the process of creating ToC. Table of content has it's own object settings, and it need to be first on the list of objects. Corresponding C code from wkhtmltopdf [examples](https://gist.github.com/matma/e5c5841324a13900c629#file-pdf_c_api-c-L74-L78).

This commit contains  "wkhtmltopdf 0.12.2" (I think it works better), some minor cleanups and whole new TableOfContentSettings. It behaves almost like in original "wkhtmltopdf" - there's an object of type TableOfContentSettings which triggers table of content creation. If there's no Xslt Transformation given, Pechkin is creating a new one like in "[wkhtmltopdf](https://github.com/wkhtmltopdf/wkhtmltopdf/blob/master/src/lib/tocstylesheet.cc)".

Test application now produces PDF document with table of content.