Add initial support for Markdown

[mingming-ma]

This commit Fixes #3 which does

The Updated Code

• Add support .md files
  • helper function bool ctil::ends_with(std::string const & value, std::string const & ending) to do extension check
    • Returns true if value string has the ending suffix
  • void ctil::generateHTML_md(std::ifstream& infile, std::ofstream& outfile, std::string filename) function to process the Markdown file
  • text file process function generateHTML is then named to generateHTML_txt and keep the logic as previous
• Add Italics parsing support for the Markdown file
  • it is converted in the void ctil::md_italics_content_update(std::string &input) function
  • find one * index and the closet next * index of the given input string, get the inner content between the *, then replace with <i>content</i>

The Updated Document

• README.md
  • Including running usage and warning for same file name special case

The Updated Examples

• Add testDirectory/markdown_test.md which contains italics syntax

Unexpected behaviour and bugs to fix

• Currently, **word** is converted to <i></i>word<i></i> which is not as expected. It should be fixed to converted to <b>word</b> in the future.

[rjwignar]

Reviewed changes.