[Feature Request] Export all files

[fcolecumberri]

When the -o option is given, Marker exports the first input file given, it can be seen here:

https://github.com/fabiocolacio/Marker/blob/eb26ca7816dcd1ca47c8c8a28263333450339776/src/marker.c#L119

However sometimes, for big documents (As an example I currently have one with 3000+ lines), it may be good reasons to split the document into multiple files and then render all at once.

So it would be nice if something like:

marker file1.md file2.md -o output.html

Would render the document as if file1.md file2.md where concatenated.

[Mandarancio]

Dear @fcolecumberri , thank you very much for your feedback, I suggest you to use the import feature of scidown that will allow to organize better huge files. however it would be possible to add this batch conversion option to marker as well. Ciao!