Change default of thread inheritance

[dktapps]

While we can't yet get rid of thread code inheritance, we can reduce its performance impact by disabling inheritance by default.

In practice, most people will rely on autoloading anyway, which is the preferred strategy, since this takes less memory and is more reliable. Code inheritance also has a massive performance cost in large applications (see #63), so this feature is just causing unnecessary slowdowns.

A more practical default setting would probably be INHERIT_INI | INHERIT_COMMENTS. (INHERIT_COMMENTS is needed for internal technical reasons - copied Runnable classes won't correctly inherit their doc comments without it).

[dktapps]

Since b81959d, the start options must be specified by the user.