Add markdown support (Lab#2)

[mismathh]

I'd like to implement two new features to this repo:

• File handling support for .md files
• Convert Heading 2 markdown syntax to appropriate HTML tags

I plan to add .md support by working within the parseArguments.ts file and wherever it checks if a file ends in .txt, I will add in another condition to check if the file also ends in .md.

In order to implement Heading 2 markdown conversion, I plan to create another .ts within the parse-markdown folder and use regex to convert Heading 2 markdown syntax into <h2>...</h2> HTML tag.

[paulkim26]

Sounds great, go for it.