Add serializer for AbstractMessage

+ Set compiler optimization flag to 0 -> easier for debugging
Remove unecessary casts

+ Check value in main fct
Merge branch 'develop' of https://github.com/jdussouillez/ShaDaPP into feature-serializer
Move src and include files in different namespaces
Rename Client in Peer
Add Serializer

- Add serializer for AbstractMessage/PingMessage/PongMessage/RequestMessage

Add deserializer for Abstract/Ping/Pong

- Change size of block info
Fix (de)serialize functions + add RequestMessage constructor for bytes
Refactoring: desezialize functions use pointer to unsigned ints
Add (de)serialization functions for Close msg
Add serializer for ResponseMessage + change data type (char* -> std::string)
Split serialization functions

- class Serializable (abstract), a serializable object must inherits it

- class Serializer, a set of static functions to serialize/deserialize integers and strings
Serialization classes in another namespace 'data'
Add serializer/deserializer for ClusterConfig
Add options parsing for config files
reformat test config file
Fix missing tag in XML
Add serialization/deserialization for Index(Update) messages
Add flags value + reformat Core.h
Fix display of version