Now that nodejs/node#3072 is mostly fixed, we can finally start using
Node 4+ features.
This refactor:
- uses arrow functions where appropriate
Note that arrow functions still aren't used in Mocha, where `this`
is sometimes meaningful.
This also removes the need for .bind() nearly everywhere, as well
as the `self = this` trick.
- refactors Validator and Connection into ES6 classes
- no longer uses Array#forEach for iterating arrays
We strongly prefer for (let i = 0; i < arr.length; i++) because of
performance reasons. Most forEaches have been replaced with for..of,
though, which is 5x slower than the long-form loop but 2x faster
than forEach, which is good enough outside of most inner loops.
The only exception is tournaments, which is due for a more invasive
refactor soon anyway.
The REPL feature has been responsible for tons of crashes, so I'm
disabling it until these crashes can be fixed.
I'm also disabling it until it actually gets documented in
`logs/repl/README.md`, because what's there right now is not
enough documentation to actually figure out how to use it.
