* [DOC] Updated the README file with info on how to create an agent.
* [SC] Agent definitions now use strings i.o. atoms for documentation.
* [DH_AGENT,DOC] Added assumptions about agents/threads/graphs.
* [DH_AGENT,DOC] Documentated agent_self_graph/1, create_agent/2, and pred_from_predspec/2.
* [DH_AGENT,FIX] Check whether the current thread in agent_self_graph/1 is indeed an agent thread.
* [DH_AGENT,SC] Simplified predicate name extraction from agent definitions.