* Removes Rc and RefCell from PreAccount
* Splits get_account() into find_index_of_account() and get_account_at_index()
in order to remove Rc from return type.
* Moves create_message(), native_invoke() and process_cross_program_instruction()
from the InstructionProcessor to the InvokeContext so that they can have a useful "self" parameter.
* Moves InstructionProcessor into InvokeContext and Bank.
* Moves ExecuteDetailsTimings into its own file.
* Moves Executor into invoke_context.rs
* Moves PreAccount into its own file.
* impl AbiExample for BuiltinPrograms
Brooks Prumo
Jack May
Alexander Meißner
Michael Vines