Additional features and QOL changes.

[ra1nlox]

I'm fascinated by this little program and I use it for my novels which I found very comfortable to write in markdown format. This being said, I found that some features I'd like to have are missing, so I implemented them myself, and thought that it would be useful to contribute it to the community (if this app has any at all, as the repo seems abandoned).

Features I added:

• Recursive directory creating for output file.
• Custom CSS class names for elements. More info in the README.
• Option to not add any cover (I hate having a placeholder cover, and I guess epub works fine without any cover at all).
• FilePreprocessor (naming to be discussed) which will probably be expanded later, adding new features, but now its only use case is to ignore and exclude obsidian tags (I personally use "#novel" at the start of my files to group them) from the final build.
• Support for symlinks (tested on Linux), which is probably useless as I found out that the program works ok without explicitly telling it to resolve the link path, but I added it anyway, for good measure.

I'm not sure that every new feature will work on any OS. I'm also not sure if I covered all edge cases, but it works for me and should continue to work.

I also consider rewriting it using click to parse arguments and integrate better with the system, maybe use some flags for options not worthy to be included in description.json like tag_new_line_style.

Let me know if the are changes or improvements to be made. My email is in the profile.