Add Environment

The idea is that the model contains an environment that it is executed
in. The environment call will contain the state and can modify it.

For now only overloaded elsewhere.

Author: wallento

riscvmodel/model.py

@@ -96,10 +96,14 @@ def commit(self):
 
         self.memory_updates = []
 
+class Environment:
+    def call(self, state: State):
+        pass
 
 class Model(object):
-    def __init__(self, variant: Variant, *, verbose = False):
+    def __init__(self, variant: Variant, *, environment: Environment = None, verbose = False):
         self.state = State(variant)
+        self.environment = environment if environment is not None else Environment()
         self.verbose = verbose
 
     def issue(self, insn):