Change the return type of vector::erase from iterator to bool

[FerdinandSpitzschnueffler]

Brief feature description

Change the return type of vector::erase from iterator to bool indicating whether the erase operation was successful.

Detailed information

In the current implementation a nullptr is returned when the provided position is invalid, i.e. out of bounds. When the last element is removed, end() is returned. Dereferencing these leads to undefined behavior. Even though validating pointers/iterators before dereferencing is the responsibility of the user we could make our code much safer when implementing the proposed change.