:lipstick:
Add .pairs file
Prevent stack overflow when subscribing in 'subscription-will-be-added'

Previously, subscribing to the same event from its first subscription
handler would cause the first subscription handler to be executed again
recursively. Now emitter keeps a subscription count separate from the
actual arrays that hold the subscriptions, allowing us to increment the
count before we add the subscription. This means when a subscription
is added in the handler, the initial subscription has already been
counted even though the handler has not been added, avoiding triggering
the first subscription event again.