Remove dependancy to extlib

This patch remove the dependency to extlib, as it makes possible to use msgpack in projects that also uses batteries. 

Only two functions were used from extlib: String.implode and String.explode. These has been re-implemented manually and are tail recursive with a O(n) time complexity.

These have been placed close to where they are used in lib/core/serialize.ml.
Also a change has been made to _oasis. 

The rest of the changes are artifacts of the fact that the repository contains auto generated files, which are updated when the project is reconfigured.