Support for Markdown files

[talkingtoaj]

Currently only Word .docx files are supported (considered the most user friendly for exam developers who are not coders), however Python is able to process Markdown much better than word documents.

We should create a base class with Word or Markdown handling as instantiated subclasses, according to the format of files detected in the input folder.

I suggest for simplicity, as a first step we should require that all files in the input folder are of the same type, and raise an error if they are not. Output file for markdown might be HTML or PDF.