README.md: added maintainer term, some typographical improvements

“Maintainer” is now the official term, “owner” is deprecated, see https://github.com/chocolatey/chocolatey.org/issues/47 and https://github.com/chocolatey/chocolatey.org/pull/49. Of course here we have the problem that NuGet’s `<owners>` tag still exists and the warmup variables also contain “OWNER”. Do you have an idea how to handle that?

Typographical improvements:
* There exists an Unicode character for ellipses: `…`
* A space needs to be added before/after the ellipsis if the word after/before is complete.
* Replaced the “typewriter apostrophe” `'` with the typographically correct apostrophe `’`.

I know, these are tiny corrections, but I really like good typography. :smiley:
It’s a pity that most of these typographically correct characters can not be written with the normal QWERT layout. But I can write them directly, because I use the [Neo keyboard layout](https://en.wikipedia.org/wiki/Keyboard_layout#Neo) instead. It’s definitely the most awesome and the most advanced keyboard layout in the world. I would never switch back to QWERT.