Update documentation for `cached` and backends

[fdegiuli]

As per https://github.com/groupon/node-cached/issues/26

[fdegiuli]

You guys don't like console statements. Should I get rid of it, or just turn it into an error instead and you can bump the version number?

[jkrems]

You can use util.deprecate. The advantage of that function is that the warning will only be logged once, not on each access. This can be important in high traffic applications where the additional output could otherwise have performance implications. E.g.:

var getDefaultName = deprecate(function getDefaultName() {
  return 'default';
}, 'The actual warning');
// ...
if (badThing) { name = getDefaultName(); }

[fdegiuli]

Never knew about that thing, thanks!

Sorry for the delay, should be fixed now.

[fdegiuli]

So much git rebase 😢

[jkrems]

Yeah, it takes some getting used to. But the automation it enables is worth it. :) Thanks for this, much appreciated! Sorry for being a bit slow to respond, busy week.

:shipit: