Feat/serialize to fix #182

[newm4n]

Added capability to Store a KnowledgeBase into stream of bytes using io.Writer and read them back using io.Reader.
I hope, this will enable user to store huge KnowledgeBase rule-set into a binary file and
read that file back into KnowledgeBase when the application start in a much faster way.

To write a KnowledgeBase already loaded in KnowledgeLibrary

func (lib *KnowledgeLibrary) StoreKnowledgeBaseToWriter(writer io.Writer, name, version string) error 

The name and version should be existing in the knowledge library.

To read a byte stream back using reader into KnowledgeLibrary

func (lib *KnowledgeLibrary) LoadKnowledgeBaseFromReader(reader io.Reader, overwrite bool) (retKb *KnowledgeBase, retErr error)

Or, if you're a hacking kind of guy, you can see example/Serialization_test.go to see how you can marshal/unmarshal a KnowlegeBase by hand.

I have not add any documentation to help user on how to do this. Help is greatly apreciated.

Oh another thing, if you use an io.Writer and io.Reader as they are, the binary size is inflated 10x-20x fold due to lots of indexing happening for the rete and generated keys, etc. So, you can wrap those Writer/Reader with archive/zip counterpart.