Only wrap handler in a bound-fn when *vertx* is dynamically bound [fixes #96]

Var.pushThreadBindings is relatively expensive, so we should only use
a bound-fn. This will break any user code that relied on that implicit
binding capture. That's easily remedied by the user passing a bound-fn
as the handler where needed.
Eliminate reflection where it can impact performance [fixes #67]
Fix API doc source links [fixes #97]