Fixed Test Makefile to run tests.

Easy to run tests now using either make test for all tests or running
make test-init, make test-user, or make src/(%).c  essentially.
Updated Readme.
Fixed Buffer length usage. Started message.c

Started creating message.c, will handle

     - Create a conversation between 2 users
     - Update a conversation between 2 users
     - High level check if message has been updated since X

Right now I've got the first slightly coded. Need to write tests for it
and such.
Started message.h

Declared prototypes:

int createConversation(const char * userA, const char * userB);

int updateConversation(const char * userA, const char * userB, const char * msg);

int checkConversationModified(const char * userA, const char * userB);