Add support for configurable Transport

needed by app engine
Split out panicwrap

Allows compiling on appengine
Add bugsnag.HandlerFunc

Like bugsnag.Handler but for HandlerFuncs
Return errors from payload.deliver
Return an error from .Notify

This lets you debug in environments where logging doesn't work (i.e.
appengine)
Take the opportunity to simplify middleware, OnBeforeNotify only for
now.
+appengine support
More conventional naming
Fix stacktrace on notifier.Notify
Use filepath glob for ProjectPackages
Fix revel with new middleware api
Include "created by" line in panic stacktrace
Update readme for new changes
v0.2