Update to libswarm 0.4.0.0

libswarm changed it's API in incompatible way, so plugin is updated
Changelog stuff.
LRU cache service added.
This is in memory LRU cache based on hash table and linked list with configurable maximum elements. It can be used to share values between different workers on single or different machines in effective manner.
The cache supports tho methods:
- put(key, value) - stores value into cache
- get(key) - retrieves data from cache in form of tuple (bool, string), where bool means that this key is present in the cache, string is the value

The asymptotic complexity of the cache is O(1) for both put and get.
Error in urlfetcher stub fixed. In post method there were get template argument that caused error. Replaced with post.
Compatibility with Core 0.10.5-5.