Add Copying file
Add sys/types.h

Having some special types are useful such as u_int32_t, uchar, and so
on.
Use -Werror flags for compile.

Treats compile warning as error to make code better.
Remove kernel image in clean target.

It might be better to remove it.
Add struct char_driver to commonize driver code.

The uart driver implement common structure to commonize driver
operations.