Add initial support for Markdown

[trangntt-016]

Hi @irenejoeunpark ,

I've just added the following features for issue #9 :

• Modify file handler so that it accepts md (1): I added a few lines of code in your main() and checks if the input file ends with ".md"

• It parses # to

  and generates a new HTML file in ./dist folder: I created a new MDUtils class which helps to process and generate MD file to HTML. The reason why I created this new file is that I don't want your Main class to have mixed responsibilities (processing both .txt and .md files) which violates SOLID principles. I think this design makes codes easier to read and maintain. Besides, I suggest you break your codes into smaller pieces so that they can be reused. For example, createHTML() can be a separate function so that it can be re-used for both .txt and .md.

• I've just updated features in your README.md

Please check it out.

Thanks