Emit error event if other error events are not listened to

[UziTech]

Emit error event if other error events are not listened to.

Currently if someone wants to catch client errors they have to subscribe to multiple error events

client.on("error", (err) => {
  assert.ifError(err);
});
client.on("setupError", (err) => {
  assert.ifError(err);
});
client.on("connectError", (err) => {
  assert.ifError(err);
});
client.on("connectTimeout", (err) => {
  assert.ifError(err);
});
client.on("connectRefused", (err) => {
  assert.ifError(err);
});

This PR will allow them to just subscribe to the error event to catch all of them but still allow them to subscribe to more if they want to.

TODO:

• Add Tests

[UziTech]

@jsumners I wanted to get your input on this before I go further. I wasn't sure if this would be too much of a breaking change.

If they weren't listening to any errors before a connectRefused, for example, would just fail silently. With this PR if there are no listeners for the error or connectRefused event than the node process will crash because of the error (Which I think is the right thing to do anyway).

[jsumners]

Seems fair to me. I could argue that this "fixes" a hole in the error handling and therefore isn't a major change.

[jsumners]

LGTM

Should we try to squeeze some docs in somewhere?

[UziTech]

It looks like only connectTimeout and connectRefused don't emit an error already if the aren't listened to. The other errors (setupError and connectError) also emit an error as well as the specific event.

[jsumners]

Ship it.

[UziTech]

Ya, I will add docs to this before merging.

[UziTech]

@jsumners what do you think about the added docs?

[jsumners]

LGTM

[jsumners]

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