Generate presenter notes

[Serhioromano]

In every slide you can add notes in <!-- --> which will not be a part of a slide but those are presenter notes.

Would be nice to add parameter like --notes that will alongside generating slides, will also generate separate TXT file with only notes in there. this way you can generate a slide and presenter notes file later to be used on teleprompter or print for hints during presentation.

[Serhioromano]

@yhatt cannot believe it! Thank you.

[yhatt]

We have to make a grateful for @chrisns's work!