One, Two, Many...

One, Two, Many... (Add ManyToOne API for configuring relationship from dependent end)

This is the equivalent API to OneToMany but for configuration of the relationship from the dependent end. It's primary use is to allow unidirectional relationships to be configured from the dependent end without needing specify the generic type and without needing to pass null for the missing nav property expression
Nit: I see you've replaced OneToMany<T>(null, xxx) with ManyToOne(xxx) which is good. But just wondering is OneToMany(null, xxx) still legal and do we still have test coverage for it (either for expected success or expected failure)?

Otherwise looks good. :shipit: