sane option parsing

Breaking changes:

 - options must be of type `object`
 - `minReq` & `maxReq` are now `min`and `max`
 - a "plugin" is injected via options.plugin, not as a mock
   being a function
 - a plugin does not override the default routes any more
hock@0.2.5
Fix clashing filteringPath and plugins

Breaking changes:
 - `{"error":"version not found"}` is returned after the limit of
   requests is reached instead of `No Matching Response!`

Closes #10