Big refactor v0.30

All test pass, except for the TestConfig suite, which is not too critical as the
plan for this version onwards is to avoid configuration as much as possible.

examples/random_delays/random_delays_sim.py

@@ -2,7 +2,7 @@
 Example of setting a 
 Example of a fully programmatic simulation, without definition files.
 """
-from soil import Simulation, agents
+from soil import Simulation, agents, Environment
 from soil.time import Delta
 
 
@@ -29,11 +29,15 @@ class MyAgent(agents.FSM):
         return None, Delta(self.random.expovariate(1 / 16))
 
 
+class RandomEnv(Environment):
+
+    def init(self):
+        self.add_agent(agent_class=MyAgent)
+
+
 s = Simulation(
     name="Programmatic",
-    model_params={
-        'agents': [{'agent_class': MyAgent}],
-    },
+    model=RandomEnv,
     num_trials=1,
     max_time=100,
     dry_run=True,