From version 5.4.0 onwards, xterm scopes its package names as
`@xterm/foo` instead of just `xterm-foo`.
We currently have a copy of xterm.css which we use instead of directly
including the one from the `@xterm/xterm` package, so I've updated the
contents of that too.
eslint is a static analysis tool that tries to identify bugs and
mistakes in the code. We have quite a variety of code in this repo so
the config is a little complicated, but I've tried to make it clear.
It's found a *lot* of issues (over 1700), and while many of which will
not be actual problems, (it doesn't like us using window properties
without `window.`,) but some definitely are.