Refactor ./bin/app.js and adding test

[tpmai22]

Fix #16

When create test case for ./bin/app.js . I have made options to become a callable function, but when I try to test it the fileFunction object which also access options function create these errors:

●  Cannot log after tests are done. Did you forget to wait for something async in your test?
    Attempted to log "This is main Error
    Error: ENOENT: no such file or directory, lstat 'C:\Users\Administrator\Desktop\repo\octo\undefined'".

      121 |       if (path.includes(".txt")) {
      122 |         return textToHTML(path, lang).then((data) => {
      126 |

      at console.log (node_modules/@jest/console/build/BufferedConsole.js:199:10)
      at bin/fileFunctions.js:123:29

To solve it, I decide to split bin/app.js to become bin/options.js and test/app.test.js . Please kindly review it