add command line options for top & left indent

[lager1]

Added options enable the user to define top and left indent of the presentation making the result more customizable. Proper implementation of slide title centering should be done. Added code assumes that the first line of any slide is the title regardless of content. Added code also somehow breaks markdown code blocks, that should also be fixed.

I'm aware that the solution is pretty hacky, but i've just wanted to add this without spending too much time figuring out how the whole program works.