Remove bitfields, which are just a bit-addressed integer

Remove bitfields, which are just a bit-addressed integer

Because we can directly map bitfields to non-byte-aligned integers, we don't
need to have a separate class type for bitfields. Merge them with integers. We
can eventually use faster read/write functions for integers aligned on byte
boundaries and which length is a multiple of 1 byte.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>