Fixed Create Conversation function.

Attempting to create a file via fopen + 'r' mode was the problem. I was
stupidly thinking to myself that attempts to open a file for reading
would also create the file. Nope. That makes 0 sense when I thought
about it and fixing said r to an a results in the test successfully
passing.
Created updateConversation method.

refactored conversation retrieval, while it does share some similar code
to the createConversation, the difference is that it does not attempt to
create the directories neccesary for the conversation to exist, rather
it returns NULL if they dont (no file pointer passed to calling party)
update conversation method tested.

Tested update conversation method, fixed to not print out to stderr and
actually print out to the file.