Multiple queries

[Masterchef365]

Allows one to make multiple queries from a single system. See the multiple_queries example!

This is a breaking change. Queries now have names; individual queries are declared like so:

sched
    .add_system(Self::update)
    .query("My Query Name")
        .intersect::<MyComponent>(Access::Write)
        .qcommit()
    .query("My Other Query Name")
        .intersect::<MyOtherComponent>(Access::Write)
        .qcommit()
    .build();

Queries are then referenced by their name:

for key in query.iter("My Query Name") {
    // ...
}