Bitfield#inspect inspect fixed, with test coverage.
AddressBus uses OffsetAccess to correctly address bank switching.
Bitfield#inspect handles Uint etc using #to_i
AddressBus raises AddressBus::OutOfBounds for address > 0xFFFF.
Refactored address_bus_spec with :accesses parameter for it_addresses.
Refactored Registers; all read/write through #[]/#[]= methods.
Uint#inspect as hexadecimal, not decimal. Also aliased as #to_s.
C64::Uint types can be added to Fixnum etc, via coercion.
Status register stored as Uint8, not Fixnum.