If a child process dies in a way that it can't recover from, the main
process now exits, to prevent loops of 'Error: channel closed'
thousands of times a second, filling up the error log and making it
hard to track down the real error.
Currently, only those features are allowed: let/const, classes, and
octal literals. More can be added when needed, as long main Showdown
server has a supporting Node.js's version.
This also accidentally fixes a bug which caused data files to not
be checked for `let`/`const` keyword existence, which would cause
a problem in a web browser.
Specifically, Users.users, Users.connections, and Users.pastUsers
are now ES6 Maps. In theory, this should be a minor performance
upgrade, but we still need to profile to make sure.
JSHint's ES6 support is shaky, and its development has stalled as of late.
Since ESLint can do by itself both JSHint and JSCS' jobs, this commit replaces them.
Gulp and its related dependencies are also hereby removed.
