There is no need to depend on the old context package now that the
minimum Go version is 1.7. The move to "context" eliminates our weird
vendoring setup. Some vendored code still uses golang.org/x/net/context
and it is now vendored in the normal way.
This change triggered new vet checks around context.WithTimeout which
didn't fire with golang.org/x/net/context.
event: address Feed review issues
event: clarify role of NewSubscription function
event: more Feed review fixes
* take sendLock after dropping f.mu
* add constant for number of special cases
event: fix subscribing/unsubscribing while Send is blocked
This commit introduces a new Subscription type, which is synonymous with
ethereum.Subscription. It also adds a couple of utilities that make
working with Subscriptions easier. The mot complex utility is Feed, a
synchronisation device that implements broadcast subscriptions. Feed is
slightly faster than TypeMux and will replace uses of TypeMux across the
go-ethereum codebase in the future.
