Reformat compton -h output

Hi,

I've long disliked the ```compton -h``` output, how it was basically a big block of text with no obvious distinction between vars and their descriptions. This aims to fix that, while making some parts a bit more concise through removal of items better left in the man pages.

As stated in my commit message, there still might be some more work to do as the new format, while being more readable, goes a decent bit beyond 80 lines, but then again ```compton -h``` currently goes beyond 80 lines at times anyways. Additionally, I removed the ```--blur-kern``` example because it was just huge, and removed the ```--vsync``` methods + explanation. mpv does something which could be implemented here, where ``--vo=help`` lists available video output methods instead of setting one.

Previously all/most commands were referred to like ```-e opacity```, but have been changed to ```-e```, as the following description states that the command talks about opacity. So that should be it, let me know what you think.