New: Added eol-last rule (Fixes #996)

`on` perf:

```
CPU Speed is 2261 with multiplier 7500000
Performance Run #1:  2853.71584ms
Performance Run #2:  2879.87336ms
Performance Run #3:  2856.63708ms
Performance Run #4:  2879.23096ms
Performance Run #5:  2874.884919ms
Performance budget ok:  2874.884919ms (limit: 3317.1163202122952ms)
```
`off` perf:

```
CPU Speed is 2261 with multiplier 7500000
Performance Run #1:  2863.81108ms
Performance Run #2:  2892.5836ms
Performance Run #3:  2906.70604ms
Performance Run #4:  2866.610639ms
Performance Run #5:  2897.305481ms
Performance budget ok:  2892.5836ms (limit: 3317.1163202122952ms)
```

Our contribution guidelines require documentation for all new rules and one sentence isn't enough to fulfill that requirement. It's really not that hard, just ask yourself some questions. Clearly you thought this rule was important enough to write, so how would you describe its importance to someone else?

Why would you want the last line to be empty? Does it help with tooling? Does it cause problems? Is this a best practice or a personal preference?

I'm sure you can come up with a few sentences.