Simulator Fixes

A bunch of simulator fixes:

• 92c835bb ("sim: Properly exit when window is closed")
• fa80679d ("sim: Fix wrong petal order")
  Fixes #68 (closed).
• 3874edb3 ("docs: Document requests dependency for simulator")
• 8a5bed0b ("sim: Mock urequests using requests")
  (If requests is not present, code without network usage still works)
• abf74077 ("sim: run: Return proper stat_result")
• 1926b535 ("sim: gc: More stubs")
• 748224fa ("Add /venv/ to gitignore")
• d6f36cfa ("sim: Fix sys_kernel re-importing host time module")

sim/fakes/gc.py

 def mem_free():
     return 1337
+
+
+def isenabled():
+    return True
+
+
+def enable():
+    pass
+
+
+def disable():
+    pass
+
+
+def collect():
+    pass