Added WIN32 ifdef around parts where needed in srcpy system code.
Updated usermessages code for Python 3.
Added ClientThink, OnDataChanged and Simulate to overridable methods in Python on the client side.
Updated C_BaseEntity to initialize the Python handle when created and also initialize the Python fields.
Added example on how to do usermessages in Python and also updated the networked entity example to modify a networked value.