Support a global database and methods that leverage it by default about entity-rs HOT 3 CLOSED

We have a builder that takes an optional database, setting it to not be None by default. We may want to tweak this to be a Weak reference instead before pursuing(see #19).

This would involve a global API, ideally exported to the top level:

• entity::global_database() would return a Weak<Box<dyn Database>> based on the internally-stored database, or just using Weak::new() if the database was not yet set.
• entity::set_global_database(...) would set some static variable containing the global reference Arc<Mutex<Option<Box<dyn Database>>>
• Generated ents would have a new() method (or something similar) that returns a builder. Internally, the new method would set the database to initially be the weak global database, although this should be able to be disabled via ent(no_global) or something similar

from entity-rs.

Global database implemented and tested. Method to produce builder prepopulated with global database is implemented but not tested.

Get and remove using global database are not implemented or tested yet.

from entity-rs.

Get is done. Still need to do remove.

from entity-rs.