Add "title" option to add a global title at the beginning of the output file

[prantlf]

If multiple files from a directory are concatenated and TOC is inserted at the beginning of the output file, a global title in front of the TOC will be missing. This pull request allows to insert the global title using the title option. If startTitleLevelAt is set to 2, only the g,lobal title will have the level 1.