Move some derived strategies into this library

[mulkieran]

Candidates are:

• StrategyGenerator from into_dbus_python - strategy that generates Python type values to match a given signature. This makes use of a small object path strategy that might have some use as well.

• _introspect.py from dbus-client-gen - strategy that generates arbitrary introspection data. dbus_python_client_gen could make use of this strategy as well. Things that should be done before the strategy is actually published are:

  • Ensure that items that the strategy generates always respect the dtd.
  • Add more configuration parameters. For example, interface_strategy takes only two parameters, which control the number of children the interface can have. Each substrategy that generates the children should have its own configuration parameters. A level of indirection might be in order.
  • Make everything that isn't necessarily exposed private.