[Review] SE-0077: Improved operator declarations

I underline that I very much rely on the Core team to pick the "right"
version of syntax.
The only opinion I have is that `greaterThan` and `above` are probably
better than `>`.

- Anton

Trent Nadeau wrote:

Although I would prefer something like:
precedence(greaterThan: LogicalAnd)
to:
precedence(> LogicalAnd)
I think the latter is more difficult to read, and I just find the idea of
using an operator in an operator/precendencegroup definition strange.

Xiaodi Wu wrote:

···

* `precedencegroup` defines both associativity and precedence, so the
naming isn't great. Maybe `operatorgroup`?
* I'm not sure about the parentheses used between the braces. To me, it
would fit better with the language to use colons.
* It may be confusing that relative precedence levels are themselves
described using operators or words that describe operators. I'd suggest
simpler words that aren't self-referential, such as "above" and "below".
So to put it all together, here's the color of my bikeshed:
```
operatorgroup Comparative {
  associativity: left,
  precedence: above(LogicalAnd)
}